investigating erythemal uv exposure and vitamin d...
TRANSCRIPT
Investigating erythemal UV exposure
and vitamin D production in the
urban canyon
Alex McKinley B.Sc.
Queensland University of Technology
Faculty of Health
School of Public Health
Thesis submitted for the degree of Master of Applied Science (Research)
4 - October - 2008
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Key words
Human health, Sun, Urban canyon, UV, Vitamin D
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Glossary of abbreviations
Ultra-violet radiation (UV), electro magnetic (EM), central business district (CBD), 7-
dehydrocholestrol (7-DHC), Australian Sun and Health Research Laboratory (ASHRL),
solar zenith angle (SZA), non-melanoma skin cancer (NMSC), parathyroid hormone
(PTH), minimum erythemal dose (MED), standard erythemal dose (SED), World Health
Organization (WHO), charge coupled device (CCD), Environmental Protection Agency
(EPA), High Performance Liquid Chromatography (HPLC)
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Abstract
Exposure to ultraviolet radiation (UV) results in both damaging and beneficial
health outcomes. Excessive UV exposure has been linked to many skin and eye
problems, but moderate exposure induces vitamin D production. It has been reported that
humans receive 90-95% of their vitamin D from production that starts after UV exposure.
Although it is possible to acquire vitamin D through dietary supplementation, the average
person receives very little in this manner. Therefore, since most people acquire their
vitamin D from synthesis after exposure to UV from sunlight, it is very important to
understand the different environments in which people encounter UV.
This project measured UV radiation and in-vitro vitamin D production in the
urban canyon and at a nearby suburban location. The urban canyon is an environment
consisting of tall buildings and tropospheric air pollution, which have an attenuating
effect on UV. Typically, UV measurements are collected in areas outside the urban
canyon, meaning that at times studies and public recommendations do not accurately
represent the amount of UV reaching street-level in highly urbanized areas.
Understanding of UV exposure in urban canyons becomes increasingly important as the
number of people working and living in large cities steadily increases worldwide.
This study was conducted in the central business district (CBD) of Brisbane,
Australia, which models the urban canyons of large cities around the world in that it
boasts a great number of tall buildings, including many skyscrapers, meaning that most
areas only see a small amount of direct sunlight each day. During the winter of 2007
measurements of UV radiation and in-vitro vitamin D production were collected in the
CBD and at a suburban site approximately 2.5km outside the CBD. Air pollution data
was obtained from a central CBD measurement site. Data analysis showed that urban
canyon measurements of both UV radiation and in-vitro vitamin D production were
significantly lower than those collected at the suburban site. These results will aid both
future researchers and policy makers in better understanding human UV exposure in
Brisbane’s CBD and other urban canyons around the world.
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Statement of original authorship
The work contained in this thesis has not been previously submitted to meet
requirements for an award at this or any other higher education institution. To the best of
my knowledge and belief, the thesis contains no material previously published or written
by another person except where due reference is made.
Signature:
Date: 25 - September - 2008
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Acknowledgements
This work could not have been completed without the help of supervisors Dr.
Michael Kimlin, Dr. Monika Janda, and Dr. Michael Moore. In addition the
assistance of the staff of the Australian Sun and Health Research Laboratory and
QUT’s Public Health department proved invaluable. Finally, Anne Herndon’s
assistance with proofreading and editing went above and beyond what one would
normally expect.
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Table of contents
TABLE OF CONTENTS 7
1. INTRODUCTION 9
2. UV RADIATION AND ITS HUMAN HEALTH IMPACTS 13
2.1. Solar UV radiation 14
2.2. Human UV exposure 21
2.3. Skin cancer 24
2.4. Vitamin D 27
2.5. Finding a healthy level of UV exposure 37
2.6. UV radiation in the urban canyon 38
3. ASSESSMENT OF UV EXPOSURE 45
3.1. Measurement of UV radiation 45
3.2. Electronic instrumentation 47
3.3. Dosimetry 50
4. VITAMIN D DOSIMETER 51
4.1. Overview of the vitamin D dosimeter 51
4.2. High Performance Liquid Chromatography (HPLC) 52
4.3. Analysis of vitamin D samples 53
5. PROJECT AIMS AND RESEARCH QUESTIONS 54
6. METHODOLOGY AND INSTRUMENTATION 55
6.1. Instrumentation used 57
6.2. Calibration of instruments 66
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7. PILOT STUDY 68
7.1. Project one 68
7.2. Project two 74
8. MAIN STUDY: INVESTIGATION OF ERYTHEMAL UV EXPOSURE AND VITAMIN D PRODUCTION IN THE URBAN CANYON 78
8.1. Study outline 78
8.2. Site selection criteria 78
8.3. Description of selected sites 82
8.4. Collection of observational data 89
8.5. Data entry and cleaning 95
8.6. Data analysis 96
9. QUANTIFICATION OF UV EXPOSURE AND VITAMIN D SYNTHESIS IN AN URBAN CANYON 97
9.1. Measurements of spectral UV radiation 99
9.2. Measurements of erythemal UV radiation 112
9.3. Measurements involving the vitamin D dosimeter 117
9.4. Measurements of air pollution and environmental conditions 128
9.5. Correlations between measurements 131
9.6. Linear regression modelling 145
10. DISCUSSION 153
10.1 Conclusions 153
10.2 Limitations and future work 157
10.3 Recommendations 159
11. REFERENCES 161
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1. Introduction
Solar Ultra-Violet (UV) radiation is electromagnetic radiation having a
wavelength between 100(nm) and 400(nm), and is a component of the natural
environment which impacts directly on human health. Over exposure to UV can cause
sun burning, various skin cancers, photo-ageing of the skin, and eye disorders, while a
lack of exposure can lead to low vitamin D production and in turn skeletal diseases such
as rickets and osteoporosis and psychiatric illness such as Seasonal Affective Disorder.
Due to the serious nature of these conditions it is vitally important to better understand
human UV exposure so as to maximize the benefits and minimize the risks associated
with it.
History of UV and human health
UV’s importance to human health is something that people have been aware of
indirectly for hundreds of years. During the industrial revolution people in low-sunlight
countries, such as England, congregated in large cities. Dark narrow streets and high
pollution levels combined to extremely limit the amount of sunlight that people were
exposed to, raising the incidence of rickets to epidemic proportions. Prevention methods
and cures did not come about however until the early 20th century, when experiments by
Sir Edward Mellanby, K. Huldshinsky, and H. Chick began to discover that exposure to
sunlight or eating certain foods could prevent/protect against rickets [1].
The 19th and 20th centuries are also when mankind began to acquire the
technology that made global transportation a possibility for the masses. New
technologies in shipping and aviation spurred great waves of relocation and colonization,
in large part by Europeans with sun-sensitive skin (their skin pigmentation evolved over
thousands of years in relatively low UV environments). These people left their ancestral
homes and moved to other parts of the planet in search of better lives, and many ended up
living in areas of the planet with very high levels of UV radiation. This relocation pre-
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disposed many of these people to skin cancer, excessive photo-ageing, and eye disorders
(the situation for the majority of the Australian population). In contrast, many dark
skinned people (whose skin pigmentation evolved to handle situations of high UV
radiation) now live in locations where at some times of the year ambient UV levels are
extremely low. These dark skinned people are now in danger of acquiring the bone
disorders associated with low vitamin D status. Due to these movements excessive or
insufficient UV exposure is a serious health concern for many people around the world.
During the 20th century a great deal of study has looked at both the positive and
negative facets of human UV exposure, ultimately resulting in a better understanding of
the workings of vitamin D as it applies to bone and mineral health and a broad grasp of
the relationship between excessive UV exposure and the development of skin cancers and
other disorders. This being said, there is still much to be learned. At present there is a
lack of consensus between researchers regarding what are adequate and optimal levels of
vitamin D, as well as what constitutes a healthy amount of sun exposure.
Factors that influence human UV exposure
The amount and type of UV that a person is subject to is dependent upon a
number of environmental factors, and in turn the outcome of that exposure is a result of a
different set of personal factors. Environmental factors that influence UV radiation
include: latitude, season, time of day, cloud cover, aerosol content (fine, solid or liquid
particles suspended in the air), and availability of shade. When UV reaches a person the
effect it has is then dependent upon personal factors such as skin colour, clothing
selection, sunscreen use, and duration of UV exposure.
The basic characteristics of the physical environment generally dictate an
individual’s sun exposure habits and use of sun protection measures. For example, warm
weather prompts people to wear less clothing in order to be comfortable, which can result
in greater UV exposure. Many people counteract this by applying sun screen, wearing
hats, or using other forms of sun protection. In contrast, cold weather prompts people to
wear more clothing, which can limit the possibility of vitamin D production. At times
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however the physical environment is more complex than these examples and the need for
a more in-depth understanding of its influences exists in order to determine if a person
may be receiving too much or too little UV.
Recent studies have shown that the modern urban environment may impact upon
both the amount of UV radiation available and the amount of vitamin D production that
occurs at street level. A Polish study [2] found that levels of UV measured in a small
urban canyon were lower than those measured at a nearby weather monitoring station
located outside of the urban canyon. Along with this, a study from Delhi, India [3] found
that young children living in an urban area known for high levels of air pollution had
lower levels of vitamin D than similar children living in an area of the city known for
relatively lower levels of pollution. These studies were both small, however their results
are compelling and show the need for more comprehensive research in relation to UV
radiation and vitamin D production within the urban canyon.
The urban canyon is important because modern lifestyle dictates that many people
spend the majority of their day-to-day lives in office buildings (behind windows and out
of the reach of UVB radiation), and at street level in highly urbanized areas. This results
in the majority of their sun exposure occurring within the urban canyon. The UV
radiation available in the urban canyon might be quite strong at times, but it can also be
attenuated by both tall buildings and air pollution, and it may be the case that at some
times of the day and/or year this UV radiation is not sufficient for vitamin D production.
Currently no distinction between exposure within an urban canyon and exposure
in other suburban or rural areas is made by policy makers or media outlets in relation to
recommendations for appropriate exposure practices or predicted UV levels. A recent
study [4] even predicted healthy exposure times for vitamin D production in major
Australian cities without mentioning the possibility of a difference between exposure
within the urban canyon and in the suburban surroundings.
The combination of a lack of knowledge associated with how the urban
environment influences human UV exposure and the growing percentage of people living
in urban areas around the world (it has been projected that over half of the world’s
population will live in urban areas by 2015) [5] constitutes a problem that needs to be
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addressed. This research takes the first step toward a better understanding of human
exposure to UV in the urban canyon.
Project overview
This study was conducted in Brisbane, Australia (27 degrees south latitude) and
consisted of the collection of observational measurements of UV radiation, vitamin D
production, and other factors influencing ambient UV levels within the urban canyon.
Data collection took place during the winter and spring of 2007 and consisted of the
measurement of erythemal UV, in-vitro vitamin D production, UVA and UVB spectra,
urban air pollution, temperature, and humidity. Measurements were taken at multiple
locations inside Brisbane’s central business district (CBD), with observational sites
having been selected with use of satellite photos and personal site examination in order to
ensure that the study locations fit the definition of an urban canyon (as described in
chapter 2). Data was also collected at a control site located just outside of the CBD to
allow comparison of observations taken in the urban and non-urban environments.
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2. UV radiation and its human health impacts
Ultraviolet radiation is electromagnetic radiation of wavelengths shorter than
those of visible light, but longer than those of x-ray radiation. Solar UV is filtered and
scattered as it makes its way through Earth’s atmosphere, however significant quantities
still reach the planet’s surface. As stated previously, excessive human exposure to UV is
linked directly to a wide range of health problems including, melanoma and non-
melanoma skin cancers, accelerated photo-aging of the skin, cataracts, and photo-keratitis
or “snow-blindness”[6]. These negative health outcomes occur because UV is powerful
enough to produce damaging changes in collagen fibres and DNA molecules in skin cells.
This same damaging energy however, is also responsible for the initiation of the
production of vitamin D within the skin. UV interacts with cholesterol in the skin
producing cholecalciferol, which is eventually converted into active vitamin D in the
kidneys and used for bone maintenance.
The duality associated with UV exposure – long-term risk of the development of
skin cancer and other problems contrasted against the body’s continual need for vitamin
D – makes it very difficult to determine exactly how much exposure is healthy for an
individual. On top of this, the fact that there is a difference between the erythemal action
spectrum and the vitamin D action spectrum (the wavelengths of UV which are involved
in the production of erythema do not entirely coincide with the wavelengths responsible
for the production of vitamin D) means that research is normally conducted through the
study of only one of the outcomes of UV exposure. This section discusses UV radiation
and the positive and negative effects it can have on human health and wellbeing.
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2.1. Solar UV radiation
What is UV radiation?
Electromagnetic (EM) radiation is energy that radiates through space in the form
of a wave as a result of the motion of electric charges. There are different types of EM
radiation, which are classified based upon the properties they exhibit and their respective
wavelengths/frequencies/photon energies; these include gamma rays, x-rays, Ultraviolet
(UV) light, visible light, infrared light, micro waves, and radio waves (figure 1). The
sum total of these different types of radiation makes up the electromagnetic spectrum,
with UV radiation occupying the segment of the spectrum associated with wavelengths
from 100(nm) to 400(nm) [6]. This is the portion of the EM spectrum associated with
wavelengths shorter than those pertaining to visible light (400(nm) – 700(nm)) and longer
than those considered to be ionizing radiation (the wavelength of 100(nm) corresponds to
the lowest energy that is required to break the weakest bond in macro molecules –
12.4(eV)) [6].
Figure 1: Electromagnetic (EM) spectrum [7]
UV radiation is further divided into three sub-categories, denoted UVA, UVB,
and UVC respectively, and these divisions are again based upon
wavelength/frequency/photon energy. The classifications are as follows: UVC –
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wavelengths of 100(nm) up to 280(nm), UVB - wavelengths of 280(nm) up to 315 or
320(nm) (different institutions have different accepted values), and UVA - from 315(nm)
or 320(nm) up to 400(nm) [8].
The sun is the primary source of UV radiation, and a small, but still substantial
portion of the sun’s total irradiated UV energy is incident on the Earth. Much of the UV
radiation coming from the sun is absorbed by the Earth’s atmosphere, however some
finds its way through and comes into contact with the surface and organisms there on,
such as plants and animals. The entire UVC band along with UVB radiation up to
approximately 290(nm) is absorbed by the atmosphere [9]. Atmospheric conditions
dictate the point at which UV is first detectable on the surface, but normally the cut-off is
between 290 and 300nm, and from there radiation of greater wavelength is increasingly
present at the surface [8]. This means, that of the radiation that reaches the Earth’s
surface, there is a relatively small amount of high-energy radiation and a relatively large
amount of low energy radiation. Figure 2 is an image of the solar spectrum taken on an
afternoon in late autumn. During this scan solar EM radiation is first visible in the UVB
range at about 300nm, a peak is found near 500nm, and radiation then decreases from
that point on past the end of the scan.
Figure 2: Solar spectrum taken in late autumn 2007 - no radiation reaching Earth's surface below 300nm and a peak near 500nm
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This figure reinforces the fact that in addition to visible light, there is a great deal of UV
radiation in the natural environment to which humans are exposed. In order to
investigate the impact this radiation has on human health it is necessary to understand the
factors that determine the amount of UV radiation found in the everyday environment.
Factors that influence the amount of UV radiation reaching the earth’s surface
The passage of UV radiation through the Earth’s atmosphere is a very dynamic
process, with various aspects having different degrees of influence as the radiation makes
its journey to our planet’s surface. The following items are of principal interest when
understanding UV radiation in the Earth’s atmosphere:
• Ozone – Ozone (O3) is created when free oxygen atoms in the atmosphere
(created when diatomic oxygen (O2) is broken apart by UV) combine with
existing O2 molecules. These O3 molecules absorb UV as it passes through the
ozone layer (thin portion of the atmosphere where the majority of O3 resides).
The ozone layer is located within the stratosphere, and although very thin, it
filters UV radiation between 200(nm) and 310(nm).
Figure 3: Location of the ozone layer in relation to the Earth and other layers of the atmosphere [10]
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This filtering occurs when UV radiation breaks apart an O3 molecule, leaving one
free oxygen atom, which quickly combines with a diatomic oxygen molecule
producing O3 again. The by-product of this process is thermal energy.
Absorption of UV by ozone begins to decrease rapidly between 280(nm) and
300(nm) and is non-existent by about the 340(nm) point [11]. Ozone can also
occur in the troposphere near the surface of the Earth. Tropospheric ozone is
created by the interactions of sunlight and hydrocarbons (created by humans) and
is considered a pollutant and can lead to respiratory disease, cardiovascular
disease, throat inflammation, chest pain, and congestion if inhaled by humans.
• High Altitude Scattering – UV radiation can be scattered or redirected on its path
toward the Earth’s surface by many substances in the atmosphere other than
ozone. Small particles (size relative to the wavelength of the UV radiation), such
as oxygen and nitrogen molecules, produce an effect known as Rayleigh-
scattering that occurs when energy from a wave is absorbed by one of these atoms
or molecules. The atom or molecule then re-emits (or scatters) this energy in all
directions, but at an intensity of 1/λ4. Rayleigh scattering occurs more at the
shorter wavelengths (UVB as opposed to UVA) [12]. Larger particles (which
have sizes similar to the wavelength of the UV radiation), such as aerosols and
water vapour also redirect UV radiation as it passes though the atmosphere [8].
This is called Mie scattering and a greater proportion of the re-emitted energy
proceeds in the same direction as the incident energy. This form of scattering is
not wavelength dependent.
• Cloud Cover – Cloud cover has a significant effect on the amount of UV
measured at a given time. Clouds are large conglomerations of water, ice, and
sometimes other molecules and therefore scatter UV in the same ways that those
particles do when they are alone. There are many different factors that determine
the exact influence clouds have, some of which are: size and shape (both
horizontal and vertical), temperature, composition, density, and altitude. Clouds
can reflect UV as well. UV can be reflected away from the Earth, but also UV
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reflecting off of the Earth’s surface and travelling out towards space can be
reflected back toward the surface again by clouds. These reflections can in some
cases produce UV levels greater than those for clear-sky conditions [8].
• Surface Albedo – The albedo, or reflectivity, of the surface environment can
greatly impact the amount of UV radiation that an observer encounters. Albedo is
defined as the ratio of reflected radiation to incident radiation. Surfaces like snow
are very reflective and can greatly increase the amount of UV observed, whereas
surfaces such as water may absorb a large amount of incident UV [8].
Generalization of Relative Surface Albedo
Relative Surface Albedo
Higher
↑
↓
Lower
Snow (Fresh)
Snow (Old)
Ice
Desert
Savannah
Forest
Water
Figure 4: Relative albedo of various surface features of the Earth
• Earth’s Orbit – During a cycle that lasts one year, the Earth travels in an elliptical
path around the Sun, meaning that its distance from the Sun is not always the
same. This changing Earth-Sun distance results in different amounts of UV
radiation reaching the atmosphere and in turn, the Earth’s surface. The difference
in UV incident on the Earth’s atmosphere due to this changing distance is
approximately 7%, between the largest and smallest Earth/sun distances [8].
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• Solar Zenith Angle (SZA) – This is the angle between the local vertical (zenith)
and the position of the sun at any given moment. When the sun is directly
overhead the SZA is 0. The SZA is constantly changing due to the earth’s daily
rotation and its orbit around the sun.
Figure 5: Solar zenith angle [13]
Larger SZAs (i.e. sun further away from the high point in the sky) mean that UV
radiation will travel through a greater amount of atmosphere therefore
encountering more ozone and other particles and lead to lower amounts of UV
reaching the planet’s surface [13]. SZAs are smaller near the equator and grow
larger as one moves toward the poles.
• Altitude – The altitude at which measurements are made can affect the amount of
UV observed. At higher altitudes UV radiation travels through less atmosphere
and therefore has less of an opportunity to collide with aerosols, O3 and other
particles. The altitude effect can vary from site to site and time to time because it
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is dependent on atmospheric conditions, such as varying O3 and aerosol levels [8].
For an alpine region (46-470N), during relatively cloud free summer days, one
study measured the differences for erythemal UV, UVA, and total radiation (300
to 3000nm) to be: 18%, 9%, and 8% respectively, per 1000m [14].
• Tropospheric Air Pollution and Aerosols – Low-level air pollution and other
particulate matter has been shown to significantly diminish measured UV levels,
especially in highly urbanized areas. A Greek study, conducted in an urban
environment (Thessaloniki, Greece, 40oN), concluded that sulphur dioxide (SO2),
a strong UVB absorber that is produced during the combustion of fossil fuels, was
responsible for almost 26% of the variability in erythemal irradiance measured
during a nearly four year period [15]. In addition, studies undertaken in Taiwan
and the US have also found urban air pollution to have an attenuating effect on
UVB radiation [16, 17].
• Tall Buildings Creating Large Shadows – Tall buildings block the sun and greatly
reduce the amount of direct sunlight reaching street level, and at many times the
only UV present in an urban area is scattered UV. Limited study has been
conducted with respect to quantifying the effect that buildings have on UV and
human exposure in their vicinity. Research has been conducted in Queensland
using smaller shade structures such as the covering over a picnic area in a park,
trees, umbrellas, and other similar objects. These different studies found that the
potential exists for an exposure of a relatively large amount of scattered UV
radiation in these situations during summer months when ambient UV levels are
very high [18-21]. One study was conducted during the Queensland winter and
concluded that depending upon the size of the structure (smaller structures
allowing greater amounts of UV) that it may be possible to receive an erythemal
dose of UV in that situation even during the winter [22]. From these studies it can
be hypothesized that, even though tall buildings in an urban environment often
block direct sunlight, the amount of scattered UV available may at times be
significant and the potential for erythema and/or vitamin D production may exist.
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2.2. Human UV exposure
Human exposure to UV can produce both positive and negative health effects. On
the positive side, exposure to UV is a necessary part of the process the human body
undertakes to produce vitamin D, however UV is also classified as a carcinogen by the
International Agency for Research on Cancer [23], and over long periods of time has
been shown to be a principle cause of skin cancer and eye disorders. UV penetrates the
skin less than a millimetre and does not reach the retina, and therefore its effects are
limited to the skin and outer portions of the eyes.
Effects of UV exposure can be divided into two categories, acute and chronic;
where acute concerns very short exposure times and chronic being on the scale of lifetime
exposure. Acute effects include tanning, sunburn, and vitamin D production, while
chronic effects include photo ageing, eye disorders, and skin cancer.
Vitamin D production is the only established benefit of UV exposure and it does
not take very long for the body to produce the necessary amount of pre-vitamin D (the
initial step in the vitamin D production process and the only one that is dependent upon
the skin’s exposure to UV radiation). It has been estimated that exposure of the whole
body to 1 MED (MED stands for Minimum Erythemal Dose, which is a unit used to
measure human exposure to UV radiation, this is described in detail in section 3.1) can
result in serum vitamin D concentrations equal to between 50 and 100 times the
recommended daily intake in Australia (currently 5 – 15 μg/day) [24]. From these
findings it has been inferred that exposure of the hands and the face (approximately 15%
of the total surface area of the body) to between 1/3 and 1/6 of an MED is sufficient for
production of adequate amounts of vitamin D.
The production of pre-vitamin D in the epidermis is limited to 10-20% of the total
7-dehydrocholestrol present (7-DHC, the compound directly involved in the production
of pre-vitamin D) [25, 26]. This finding has been shown to be independent of how long
the skin is exposed to the sun and is due to the fact that UV radiation begins to break
apart newly produced cholecalciferol during extended exposure. 10-20% of the 7-DHC
present in the skin can be converted into pre-vitamin-D prior to receiving an erythemally
damaging amount of UV radiation [27], thus excessive exposure is not even beneficial for
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the production of vitamin D. These previous facts mean that it is possible for a person to
manage their UV exposure in such a way as to maintain healthy levels of vitamin D
without exposing themselves to the risks of overexposure, assuming the availability of
sufficient ambient amounts of UV radiation. It has even been reported that the theoretical
burden of disease that is avoided by exposure of the skin to UV radiation is possibly
greater than that due to over exposure [28, 29].
The chart below expresses the need to find a healthy balance between over and
under exposure to UV radiation by depicting the way both excessive UV exposure and a
lack of UV exposure increase burden of disease.
Figure 6: UV exposure vs. relative burden of disease, healthy exposure results from vitamin D production and limited skin damage
In order to determine what a healthy level of UV exposure is it is necessary to
understand how UV radiation produces different health outcomes when it interacts with
the human body. The erythemal and vitamin D production action spectra are used to
describe ambient UV radiation in terms of the health outcomes they produce.
Relationship Between UV Exposure and Relative Burden of Disease
Decreasing
UV Exposure
Increasing
Increasing
Decreasing
Burden of
Disease
Healthy Exposure
Reduced Exposure Excessive Exposure
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Erythemal action spectrum versus vitamin D production action spectrum
An action spectrum is a parameter that describes the relative effectiveness of
different wavelengths of energy to produce a specific biological response. In this case
shorter wavelengths produce a greater biological response and therefore they are
weighted more heavily than longer wavelengths as can be seen from figure 7. The total
dose is calculated by integrating over the entire wavelength range. Wavelengths of UV
do not produce erythema and vitamin D equally in the human skin, and for this reason
there are different action spectra. The wavelengths of radiation that cause erythema also
cause photo-aging and skin cancer, so the erythemal action spectrum can be thought of as
the action spectrum for negative outcomes of UV exposure [30].
Figure 7: Action spectra for pre-vitamin D (right axis) and erythema (left axis) [30]
UV below 320nm makes up the majority of both action spectra, however erythema is still
produced (to an increasingly lesser degree as wavelength increases) by UV up to 400nm.
Vitamin D production however, is focused around wavelengths 295-300nm and is non-
existent upwards of 320nm [25]. For these reasons it is possible to find situations where,
although direct sunlight is visible the production of vitamin D is not possible because
there is no UV of wavelength 320nm or lower present. These situations are generally
encountered at high north or south latitudes during the winter months. In addition, the
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differences between these two action spectra mean that it is very important to not take
measurements of erythemal UV as proof of vitamin D production.
2.3. Skin cancer
Skin Cancer Background
Skin cancer is a condition in which normal, healthy skin cells become malignant
and experience uncontrolled growth. Skin cancer has been linked to exposure to UV
radiation [6]. The outer layer of skin is home to three types of cells, squamous cells,
basal cells, and melanocytes, and each of these can develop into cancer. Cancer that
develops in either the squamous or basal cells is termed squamous cell or basal cell
carcinoma (non-melanoma skin cancer - NMSC), while cancer that develops in the
melanocytes is termed melanoma [31]. Both melanoma and non-melanoma skin cancers
are more prevalent in individuals with fair skin, and studies have also shown higher
incidence rates to be associated with decreasing latitude (implying that skin cancers are
more prevalent in areas of high UV exposure) [31, 32].
Chronic exposure to UV radiation is an important factor in the development of
NMSC in humans [6, 33, 34], with the majority of NMSC occurring on the head, neck
and forearm areas. NMSCs can be divided into sub-categories and both chronic and
intermittent exposure to UV radiation has been linked to the development of these
various sub-groups [35, 36]. In the development of melanoma it is believed that long-
term exposure to UV radiation does not have a great effect. Instead, intermittent, intense
exposure, to non-acclimatised skin can influence the development of melanoma [37].
This is especially predictive if intense exposure occurs at a young age [38]. Unlike
NMSC, melanoma is more likely to occur on parts of the body that are not normally
exposed to the sun. This finding has yet to be scientifically explained. Phenotypic risk
factors have been linked to both melanoma and NMSC, with some of these being – light
eye colour, fair complexion, light hair colour, tendency to sunburn, and poor ability to tan
[39].
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Skin cancer in Australia
Australia has the highest rates of skin cancer in the world [40]. With over
380,000 Australians being treated for skin cancer each year, this accounts for 83% of all
new cancers diagnosed in the country. Of all states in Australia, Queensland has the
highest rates of skin cancer in Australia, making the “Sunshine State” also the skin cancer
capital of the world, with the treatment of skin cancer costing Australians around $300
million each year [39].
Skin cancer of all forms is a very serious public health issue in Australia, where it
has been established that half of all residents will be diagnosed with some form of skin
cancer during their lifetime. Of the cancers that are diagnosed, up to 95% of cutaneous
melanomas, and 99% of squamous and basal cell carcinomas have been established to be
caused by solar UV radiation [40, 41]. There exist two main factors that combine to
produce the extreme rates of skin cancer found in Australia: extremely high levels of UV
and the fact that the majority of the population has very sun-sensitive skin. It is not
uncommon for the UV index (a scale developed by the World Health Organization that
grades the danger of exposure to solar UV radiation, which is described in detail in
section 3.1) in many Australian locations to be well into the ‘extreme’ range of the scale
for the majority of the day. In addition, most non-indigenous Australians come from
northern European heritage, meaning that the climate in which they live is much different
than that for which their skin pigmentation evolved. The lighter skin of Europeans
developed over thousands of years in a climate that was subject to much lower levels of
UV. This sun-sensitive skin allowed the European ancestors of modern day Australians
to produce healthy levels of vitamin D in a climate of low UV radiation, however it now
predisposes much of the Australian population to the negative health outcomes associated
with excessive UV exposure.
Prevention efforts and increased incidence
The negative health outcomes of excessive UV exposure have been known for
quite some time, and serious efforts to educate the public about these risks have been
26
made in Australia. Over the past 20-30 years governments and other organizations have
used campaigns (such as “Slip, Slop, Slap” – Cancer Council of Australia [42]) to
promote healthy exposure practices. Many of these campaigns are aimed at promoting
healthy sun exposure practices in younger populations. Even with these campaigns in
place skin cancer rates have increased over the past few decades [43]. A portion of the
higher incidence rates may be a result of increased screening [44, 45]. In addition, it has
been found that incidence rates for Australians under 60 (many of whom were exposed to
skin cancer prevention campaigns during their youth) have begun to stabilize in recent
years [46].
Along with an increase in incidence due to greater screening, researchers are also
beginning to find an increase in incidence associated with the rise in popularity of sun
bathing and artificial tanning through the use of tanning beds [47-49]. Social trends have
made being tan very popular for lighter skinned populations, especially among teenagers,
and it is believed that this practice may severely impact future rates of skin cancer in
many countries. Tanning beds use differing amounts of UVA and UVB radiation in
order to produce an increase in the amount of melanin pigment in the skin, and some state
that they are safer than others due to the use of UVA radiation in lieu of UVB [50].
Research has yet to determine the validity of these claims. In any of their forms, the tan
produced is not a very effective protection against sunburning when compared to the risk
of long-term accumulated exposure to UV. Tanning beds have only been in use for the
last 10 to 20 years, and because skin cancer is a condition that takes many years to
present, research associating the risks of their use to increased incidence of skin cancers
is not readily available.
27
2.4. Vitamin D
What is vitamin D?
The first scientific encounter with vitamin D occurred when hypovitaminosis D
was observed at the end of the 19th century in cities of the industrial revolution, most
notably those in low sunlight countries of northern Europe. Lack of vitamin D
production from UV exposure was the cause behind the dramatic rickets epidemic that
struck the narrow, polluted, and dark streets of cities such as London and Warsaw during
this time period. Research by Mellanby, McCollum, Huldshinsky, and Chick et al. [1,
51] independently found that cod liver oil and exposure to UV (direct sunlight and
artificial) were able to quickly cure the disease in both humans and animals, however the
workings of these cures were not fully understood. At first it was thought that vitamin A
was the compound responsible for the recovery, eventually however vitamin D was found
to be different from vitamin A, and was therefore classified as vitamin D – the fourth
vitamin. When vitamin D was first discovered it was classified as a vitamin because of
the human body’s reliance on it, just as had been done with vitamins A, B, and C earlier.
More advanced science has determined that vitamin D is actually a seco-steroid [52], and
that there exist two naturally abundant forms [1].
The term ‘Vitamin D’ is a generic term, which refers to a molecule that has the
general structure of either of two biologically inert precursors to the active form of
vitamin D - vitamin D3 (cholecalciferol) or vitamin D2 (ergocalciferol). These structures
are shown in figure 8.
28
Figure 8: Structure of vitamin D2 (left) and vitamin D3 (right) molecules [53]
Technically these substances are classified as seco-steroids, because the B-ring of the
carbon chain has a broken bond. Both vitamin D2 and vitamin D3 are biologically
inactive and need hydroxylation reactions in the liver and kidneys to produce 1,25-
dihydroxyvitamin D (1,25-[OH]2D or calcitrol), which is the biologically active form of
the substance [52].
Physiology of vitamin D
The principle physiologic function of vitamin D is to facilitate absorption of
calcium from the diet within the intestine, which is then used for bone maintenance and
support of nerve and muscle function. 1,25(OH)2D acts by stimulating the expression of
a number of different proteins that assist with calcium transport from the intestine into the
bloodstream, the most notable of these being calbindin. If the body does not have enough
calcium in the bloodstream it attempts to increase circulating calcium levels by releasing
PTH. PTH has three functions that compensate for insufficient intestinally derived
calcium: mobilization of calcium from bone, inducing the production of 1,25(OH)2D in
the kidney, and the suppression of calcium wasting in the urine [52].
29
Figure 9: The three ways that PTH works to increase the concentration of calcium in the blood [54]
When circulating calcium levels are below normal the body extracts calcium from
stores in the bones in order to sustain nerve and muscle function, meaning that having a
healthy level of vitamin D is related to bone health through its promotion of calcium
absorption in the gut. Vitamin D also works in concert with a number of other vitamins,
minerals, and hormones to promote bone mineralization [55], which is the process in
which mineral is added to the already formed bone matrix. Vitamin D has also recently
been shown to have possible ties to a number of other processes, such as suppression of
cancerous cell growth - these will be discussed further on.
How do humans acquire vitamin D?
Vitamin D3 is produced in the skin after UV exposure, but can also be ingested,
while vitamin D2 can be obtained from the diet in the form of plant sources. Humans
acquire the majority of their vitamin D through cutaneous production after UV exposure
and dietary intake is not necessary if sufficient amounts are produced in the skin.
When UV photons of wavelengths 290-315nm come into contact with 7-
dehydrocholestrol in the plasma membrane of skin cells the process that eventually
results in the production of biologically active vitamin D is initiated [51]. This process
30
begins when UVB radiation breaks the 9-10 carbon bond in the B-ring of a 7-DHC
molecule in the skin, producing pre-vitamin D3 [52]. After the initial reaction, a
thermodynamic process occurs in which, pre-vitamin D3 (an unstable isomer) is
transformed through a rearrangement of double bonds into biologically inactive vitamin
D3 (or cholecalciferol) [52]. In order for the body to make use of vitamin D (either D2 or
D3) it must first be metabolized in the liver and then again in the kidneys, so from the
skin it passes through the cell wall and into the bloodstream and on towards the liver.
Vitamin D is a hydrophobic molecule in each of its forms and is aided in its journey
through the bloodstream by a carrier protein, appropriately named the vitamin D binding
protein [51]. Figure 10 describes this process.
Figure 10: The path of vitamin D production in the human body [56]
Upon reaching the liver cholecalciferol is hydroxylated by the enzyme 25-
hydroxylase into 25-hydroxycholecalciferol (also, ‘25 (OH) vitamin D’ or ‘25(OH)D’)
[52]. 25(OH)D then serves as a substrate for 1-alpha-hydroxylase in the kidney, where
31
the resulting biologically active form of vitamin D, 1,25dihydroxycholecalciferol (also
‘1,25(OH)2’ vitamin D or ‘1,25(OH)2D’) is produced [52]. The half-life of 25(OH)D is
several weeks while the half life of 1,25(OH)2D is only a few hours. Along with this
short half life, the amount of 1,25(OH)2D present in the human body at any given time is
extremely low and is closely regulated by parathyroid hormone (PTH). On the other
hand, the amount of 25(OH)D circulating in the blood stream is indicative of the amount
of storage vitamin D that the body has made from recent cutaneous production or
ingestion. These factors make it difficult to accurately measure vitamin D status through
1,25(OH)2D, and therefore 25(OH)D (the more prevalent , but biologically inactive
storage form of vitamin D) has become the accepted measure of a person’s vitamin D
status.
It has been stated that exposure of the entire body to 10–15 minutes of midday
sun in summer (thought to be equal to about 1 MED – discussed in section 3.1) is
comparable to taking a supplement of 15,000IU/375μg of vitamin D [57]. From this it
has been extrapolated that 1/3 of an MED can be acquired by exposing the hands, face,
and arms to this same amount of sunlight with the result being a healthy amount of
vitamin D production (what constitutes a healthy amount of vitamin D is discussed
further on in this section). This finding has been cited frequently during the past decade,
and while based upon sound research, has yet to be rigorously proven. Important factors
such as skin colour and intensity of UV radiation have not been incorporated into this
recommendation of ‘10-15 minutes of summer midday sun’ and therefore it is not
something that should be considered to apply to all people in all situations.
In the case of dietary acquisition, the most notable sources of vitamin D are cod
liver oil, salmon, mackerel, tuna, egg yolks, and foods that are fortified with either D2 or
D3 (in most cases D3) such as milk [58]. The fortification of foods with vitamin D is
most notable in the United States and does not happen at all in many parts of the world,
including Australia. It has been shown that vitamin D obtained through dietary means is
a successful way to prevent vitamin D deficiency [59, 60], however it is not necessary.
For persons not living at extremely high latitudes large enough quantities of vitamin D3
can be produced by the body through exposure of the skin to UV that sustainable healthy
vitamin D levels can be maintained [61] without dietary intake.
32
How is the amount of vitamin D in the body measured?
Measuring the amount of vitamin D in a person’s body is somewhat difficult, as it
is only possible to measure vitamin D status by drawing blood. When blood is drawn, the
amount of 25(OH)D in the serum is measured and results are disseminated in units of
either ng/mL or nmol/L. What exactly constitutes an insufficient or deficient level of
25(OH)D in the human body is subject to debate. Deficiency has been classified as
having 25(OH)D levels of less than 20 or 25 nmol/L and insufficiency has been classified
as having 25(OH)D levels of anywhere between 35 to 50 nmol/L upwards to between 80
and 100 nmol/L. Sufficiency is generally thought to be anything above these varying
insufficient levels, with the most notable characteristic being that someone having a
sufficient level of vitamin D will not show any of the symptoms of the diseases
associated with below healthy vitamin D levels [62].
Wolpowitz and Gilchrest give an exhaustive review of the current state of this
debate in their paper “The vitamin D questions: How much do you need and how should
you get it?” [62], and a summary of this can be seen in table 1.
Vitamin D status and associated characteristics
Table 1: Summary of vitamin D status categories [62]
Different theories have been presented as to how vitamin D status levels ought to
be determined, with two main avenues standing out: measuring the status of people who
33
spend a great deal of time in the sun and taking their levels as sufficient, or taking the
levels at which certain biological functions occur as the cut-offs between different
categories of vitamin D status. The first school of thought stems from the fact that
humans evolved in equatorial regions with sunny climates and did not wear a great deal
of clothing, therefore it is assumed that a healthy level of vitamin D would be obtained by
someone who spent a large amount of time in the sun [63]. Following this reasoning, it
has been proposed that the 25(OH)D levels of lifeguards might be a good measure of
sufficient vitamin D status. The other side of the debate is based upon the fact that
vitamin D regulates calcium absorption and that low levels of calcium induce PTH
production. It has been suggested that an accurate measure of a lower bound of sufficient
vitamin D status might be that at which anything less produces a rise in PTH
concentration, and that an upper bound of sufficient vitamin D levels might be that at
which an increase in 25(OH)D no longer increases calcium absorption [62].
When assessing the vitamin D status of the public, studies generally focus on
various groups of at-risk populations, such as those living at high latitudes, the elderly,
and veiled women. Contemporary studies have documented insufficient or deficient
levels of vitamin D around the globe, and include some of the following findings: a US
survey of women age 15-49 found that 41% of African American women and 4% of
Caucasian women were vitamin D deficient at the end of summer [64], a study of medical
personnel in Boston observed that at the end of winter 36% of the study population was
vitamin D insufficient [65], a Finnish study found that of a group of 10-12 year old girls
32% were vitamin D deficient and 46% had insufficient vitamin D status [66], and
finally, recent Australian studies have reported finding vitamin D deficiency rates of 43%
in young women and 23% in the general adult population [67, 68]. In addition to these
results, a recent ASHRL study found that 42.5% of the study participants had insufficient
or deficient levels of vitamin D [69].
In general, the results of these studies have shown that there may be more people
around the world living with poor vitamin D health than previously suspected, however
there is much work that needs to be done in terms of both defining exactly what is low
vitamin D status and determining who is at risk. It is almost universally agreed upon by
researchers that currently used cut-offs of 25(OH)D associated with ‘deficient’,
34
‘insufficient’, and ‘sufficient’ levels of vitamin D status need to be reassessed.
Increasing the levels of 25(OH)D associated with these categories would raise the
number of people considered to have sub-optimal levels of vitamin D. In reality vitamin
D insufficiency is probably more prevalent than is shown in current literature. In relation
to this it is also the opinion of many researchers that the recommended vitamin D intake
levels given by many governmental health organizations are too low [70].
Consequences of hyper or hypo-vitaminosis D
It’s very difficult to acquire too much vitamin D. During a single prolonged
exposure to UVB, cutaneous pre-vitamin D3 production does not exceed 10-20% of the
original 7-DHC present in the skin [25, 26]. Only 10-20% of the 7-DHC in the skin is
transformed into pre-vitamin D because once pre-vitamin D3 is produced, it can either
isomerize into vitamin D3 or it can absorb more UVB and isomerize into the biologically
inactive photo-isomers such as lumisterol or tachysterol. Along with this, vitamin D3
itself can also absorb UV and isomerize into one of a number of different photoproducts
[25].
Figure 11: UV breaks the B-ring of 7-DHC to form Pre-vitamin D3. Thermal isomerisation then produces 25(OH)D. However, if exposure persists tachysterol, lumisterol, or other photoproducts result [71].
35
Through these pathways the human body is able to limit the amount of vitamin
D that is produced in the skin, meaning that excess UV exposure does not result in
intoxication [72]. Studies have also shown that excess supplementation normally does
not lead to intoxication because the dose that this would require is enormous [24, 72-74].
The most likely cause of hypervitaminosis D would be an industrial accident in which
pills were incorrectly formulated. The symptoms associated with vitamin D intoxication
are minor and include dehydration and vomiting.
The risk of receiving too little vitamin D is a much more realistic possibility, and
the consequences of vitamin D deficiency are much greater than those of intoxication.
These consequences result from raised PTH levels (a condition termed secondary
hyperparathyroidism, and generally defined as PTH levels greater than 65 pg/mL [62]),
and include rickets in children, and osteomalacia in adults. These diseases are similar
and involve a softening of the bone structure and an eventual breakdown of the bone
matrix. Both occur when a lack of calcium absorption from the gut leads the body to
make use of calcium stored in the bones in order to maintain normal muscle and nerve
function. Physiologically, bone structure is continually being torn down and remade, but
without absorption of sufficient dietary calcium the body forgoes the addition of calcium
to the bone structure and instead uses calcium taken from the bone structure for the
support of more urgent functions resulting in rickets or osteomalacia [62].
Rickets is a disease that was not overly prevalent until the start of the Industrial
Revolution. During that period children living in the newly industrialized cities of
Europe and North America began to develop rickets at alarming rates. By the end of the
19th century the disease had grown to epidemic proportions and it was estimated that
upwards of 90% of the children who lived in the industrialized cities in those
aforementioned regions had manifestations of rickets [75]. In fact the problem became so
bad in England (which is an area that already does not see large amounts of sun-light)
that the disease became know as “the English disease”. The problems associated with
rickets are related to bone deformation and typically result in bowed legs and other
skeletal problems. Osteomalacia has a less storied history, but is still a very significant
problem, which is associated with bone and muscle pain along with falls and fractures
that are often times serious and debilitating. Osteomalacia is most prevalent in elderly
36
populations and has been linked to increased risk of hip and other fractures [76-78]. It
has been recommended by many studies that supplementation of vitamin D and calcium
can reduce the risk of these falls and fractures in the elderly [79, 80].
Most frequently, the contraction of rickets or osteomalacia stems from a lack of
vitamin D, but can also be due to extremely low levels of dietary calcium, and kidney or
liver disease. An example of this is the documentation of extreme cases of rickets
involving children in equatorial Africa who were inarguably vitamin D sufficient, and
who were completely cured with calcium supplementation alone [81].
Vitamin D beyond rickets and osteomalacia
1,25(OH)D may play an important role in cancer prevention through the
regulation of cell growth. In 1941 it was first reported that sun exposure had a protective
effect in relation to many forms of internal cancers [82]. It was found that people living
in the north-eastern part of the U.S. were more likely to die from internal cancers (breast,
colon, and prostate cancers for example) than people living in the southern part of the
country, however people living in the south were more likely to acquire non-life
threatening forms of skin cancer. This finding led researchers to theorize that skin cancer
had a protective effect against other forms of cancer. Over time similar results were
found in ecologic studies from many different parts of the world and this phenomena is
reviewed in “Epidemiology of disease risks in relation to vitamin D insufficiency” [83]
and “Solar Power for Optimal Health” [84].
For years it was believed that sun exposure was the reason behind these
differences in cancer rates, but the mechanism was not understood. Vitamin D is now
thought to be that mechanism. Cells in many different parts of the body (skin, colon,
prostate, breast, skeletal muscle, brain, monocytes, and activated T and B lymphocytes
for example) have vitamin D receptors [85]. Since the first discoveries of vitamin D
receptors in different cells, it has been shown that the cells of the colon, breast, and lung -
among others - express the 1-alpha-hydroxylase necessary for conversion of 25(OH)D
into 1,25(OH)D. These two discoveries are very important because they mean that
37
vitamin D may play an important role regulating the growth of many of these different
types of cells. These cells are able to accept 25(OH)D that is circulating in the
bloodstream with the vitamin D receptor and then hydroxylate that compound into its
bioactive form 1,25(OH). The account of these discoveries is reviewed by Holick in,
“Vitamin D: Its role in cancer prevention and treatment” [85].
2.5. Finding a healthy level of UV exposure
Balancing the risk of skin cancer with the risk of vitamin D deficiency is an
important issue that currently sees many differing viewpoints around the world.
Researchers from higher latitude locations in the northern hemisphere tend to focus their
work on the positive effects of increased sun exposure [86], whereas academics in
Australia generally focus on the sun protection and vitamin D supplementation side of the
issue [41, 49].
The researchers promoting increased UV exposure contend that the danger of
vitamin D deficiency combined with the possible benefits of cancer prevention
overshadow the dangers posed by skin cancer, and suggest that current personal exposure
guidelines are promoting too much sun avoidance and that many people would benefit
from increased sun exposure [72, 73, 84]. The other camp however, feels that the
campaigns used over the last 20-30 years (“Slip, Slop, Slap” – Cancer Council of
Australia [42], “Play Safe in the Sun” – Women’s Dermatological Society (U.S.A.) [87],
“Block the Sun, Not the Fun” – Sun Safety Alliance (U.S.A.) [88], etc… ) have taken
root in society and a drastic change to the overall message would cause confusion and
result in an increased incidence of skin cancer that would far outweigh any gains in
vitamin D health. This second group would promote dietary supplementation as a
solution to low vitamin D status instead of increased sun exposure during periods of
intense UV, and only during winter months at higher latitudes would sun protection
measures be relaxed [89].
38
The key to finding common ground and developing a useful public health message
is continued research, a point that is made clear by Craig Sinclair, of The Cancer Council
Victoria, in his recent article: Risks and benefits of sun exposure: Implications for public
health practice based on the Australian experience, [90] where he states,
“The most difficult factor in coming to an agreed position statement has
been to determine what would be a reasonable level of radiation necessary
for healthy bone growth and development that will not add to substantial
risk of skin cancer. It was clear among OA [Osteoporosis Australia],
ANZBMS [Australia and New Zealand Bone and Mineral Society], and the
ACOD [Australasian College of Dermatologists] that we are still a long
way from having sufficient evidence to suggest where this point should
exactly be. This difficulty exists almost entirely due to the limitation and
paucity of existing research.”
This project adds to the knowledge base by investigating the effect the modern day urban
environment has on UV exposure levels and vitamin D production.
2.6. UV radiation in the urban canyon
An urban canyon is a man made environment consisting of streets cutting through
dense blocks of multi-story buildings, especially skyscrapers. Urban canyons are densely
populated and commonly have a great deal of human traffic.
The structure of the urban canyon combines with the traffic patterns to create a
distinct set of environmental conditions. The height of the buildings diminishes the
amount of direct solar radiation reaching the surface and the large amount of automobile
traffic creates air pollution. This environment is often times very different from other
nearby areas.
39
For the purposes of this study and for comparability with other work, an urban
canyon will be defined using the following criteria for any given one block section…
1. At least 50% of each side of the street is bordered by buildings of no less
than 5 stories.
2. No more than 30% of each side of the street is bordered by buildings of 2
stories or fewer.
3. At least 3 streets fitting the above description are found within a 1.5km2
area.
Research into the health effects of UV in the urban canyon
A small number of studies have investigated the impact of the urban environment
on UV radiation and vitamin D production, however no study to date has considered
these simultaneously. Results of these studies have shown either lower amounts of UV
radiation or lower levels of vitamin D production in highly urbanized areas in relation to
nearby less urban locations. One finds from personal experience that UV levels can be
variable in an urban environment with many tall buildings, but scientific data backing this
observation up and relating it to the negative health outcomes of UV exposure or
production of vitamin D is lacking.
There have been three relevant studies to date, with the first being an Indian
project that looked at vitamin D levels in young children from two distinct
neighbourhoods – one known for high levels of air pollution and another that was thought
to have cleaner air [3]. Second, a Polish study measured UV at street level in an urban
canyon (the only study that has done this) and compared these readings to measurements
taken at a nearby location outside of the urban canyon [2]. And finally an Australian
study that used past UV data to calculate exposure times necessary for the synthesis of a
sufficient amount of vitamin D in different Australian population centres at different
times of the day and year [4]. The Indian and Polish studies both collected small
amounts of data and were obscure in nature, while the Australian study made no
40
distinction between the urban canyon and the surrounding area. These studies are
discussed in detail in the following pages.
In addition to these three studies various works have investigated the impact that
air pollution has on solar radiation. Some of these have dealt with pollution produced by
industrial activities and automobile traffic, while others have focused on naturally
occurring phenomena such as smoke plumes from forest fires. Of these, a number used
data from meteorological stations outside of urban areas, and none collected data at street
level in the urban canyon, limiting their value in terms of this project.
Three principle studies investigating human exposure to UV radiation in the urban
canyon
● In 2000, Agarwal et al. [3] conducted a cross sectional study in which the
25(OH)D and PTH blood serum levels of infants and toddlers from two different parts of
Delhi, India were measured. The study sites were Mori Gate and Gurgaon. Delhi is one
of the most polluted cities on the planet and the area of Mori Gate is known for relatively
high levels of air pollution even in that region. The area of Gurgaon lies on the outskirts
of the metropolitan area and is regarded as having lower levels of pollution than Mori
Gate. The researchers hypothesized that children living in the area of higher pollution
would have lower levels of serum 25(OH)D and higher levels of PTH than the children
living in the low pollution area. Findings of this nature would indicate a relationship
between higher levels of air pollution and lower levels of vitamin D production,
indicating that the air pollution in Mori Gate was attenuating a significant amount of UV.
Twenty six children aged 9-24 months from Mori Gate were age-matched with 31
children from Gurgaon. The paper does not state why this age range was chosen. These
were both low-income areas of the city, and the living conditions were similar in each
area, with most of the children living in single story, one-room houses. The diets were
very similar in each area, and contained almost no vitamin D. None of the children took
a vitamin D supplement, so nearly all of their vitamin D was due to cutaneous
production. The time the children spent in the sun was not measured.
41
Pollution was measured by a haze-sensor with accompanying filter that only let
wavelengths 285-310nm pass, and via this measurement, it was determined that there was
a higher level of air pollution in Mori Gate than in Gurgaon, implying that there was also
less solar UVB reaching the Earth’s surface in Mori Gate than in Gurgaon. However,
direct measurements of solar UV radiation were not collected.
The study found that the children living in the Mori Gate area did have lower
mean serum 25(OH)D3 levels: 11.7ng/mL in Mori Gate compared to 27.1ng/mL in
Gurgaon (p<0.001). Along with this, higher mean PTH levels were found in the children
from Mori Gate: 25pg/mL in Mori Gate compared to 13.1pg/mL in Gurgaon (p<0.01).
From these results it was concluded that since the children’s diets were very similar the
disparity in vitamin D status and PTH levels was most likely due to a difference in UV
exposure caused by urban air pollution.
The results of this study provide a basis for further research by showing that air
pollution may in fact have an effect on the cutaneous production of vitamin D. However,
there were a number factors associated with this study that limit its value.; the cross-
sectional nature of the study, the use of a filter that attenuated radiation between 285 and
310nm (it is thought that UV of wavelength 290-315 is capable of producing vitamin D
in human skin [25], and the lack of a measure of the subject’s UV exposure being the
most notable.
• The second study, conducted by Podstawczynska and Pawlak [2], is a comparison
between measurements of UV levels taken in the urban canyon of Lodz, Poland and at
nearby Lipowa meteorological station. This study measured UV 290-400nm and total
solar radiation at four sites in the urban canyon as well as at Lipowa station on four
separate days during the summer of 2002. Data was recorded using Kipp & Zonen
broadband radiometers model CUV3 and CM11 set up on a tripod 3 meters from the wall
of the urban canyon. Measurements were taken on either side of an east-west street and
on either side of a north-south street in areas where building height to street width ratios
were between 1.1 and 1.5, which roughly equates to buildings of 4 - 7 stories (this is
approximated from the data given in the article: street width was 13.7 – 18m, and an
assumption of 3m per story).
42
This study found that the obstruction of direct sunlight was the major factor
influencing the amount of both UV and total solar radiation measured in the urban
canyon. The measured levels of UV and total solar radiation in the urban canyon were
significantly lower than those measured at the Lipowa site for nearly all but the direct
sunlight conditions. Two hours was the greatest amount of time that any of the sites saw
direct sunlight during a single day, and one site saw no direct sunlight during the entire
experiment. For nearly the entire study, the measured radiation levels were lower in the
urban canyon than at the nearby meteorological station.
The results of this study provide support for the hypothesis that the urban canyon
can reduce UV levels and this in turn may reduce vitamin D production capability for
people who spend significant time in the urban environment. However, as with the
previously discussed study, this work had significant limitations. Data was only collected
for four days and there is no specific measure of the portion of the spectrum for which
vitamin D is produced (290-315nm), so one cannot make any direct assumptions
regarding the attenuation of vitamin D-producing UV. Even with these limitations the
results are very compelling, especially considering the relatively low building height at
the study locations.
● The final study was conducted in Australia [4] and investigated seven different
cities using surface UV radiation measurements. These measurements were converted
into times needed to obtain 1 MED for someone of Fitzpatrick skin type II (Fitzpatrick
skin type is discussed in section 3.1), and used to propose guidelines for healthy sun
exposure times in each city during all twelve months of the year.
It was reported that in Brisbane (27 degrees south) it took 2-6 minutes in the
summer and 5-14 minutes in the winter to obtain sufficient, but not harmful, levels of UV
radiation (according to the criteria laid out in the study). In Hobart (much farther south –
at latitude 42 degrees south) it was reported that in the summer, sufficient but not harmful
levels of UV radiation could be obtained with 7-14 minutes of exposure, and that in the
winter 37-110 minutes were needed. Other cities studied were: Townsville, Perth,
Sydney, Adelaide, and Melbourne.
43
This study is interesting, but has notable issues, the first being that the action
spectrum for production of vitamin D is not the same as that for erythema (as discussed
previously), meaning that the results pertaining to erythema cannot be assumed to be
accurate for predicting vitamin D production. Another point of contention is the
hypothesis that vitamin D production may be very different between highly urbanized
environments and suburban or rural environments. This study makes no distinction
between the two – when in fact it may not be appropriate to make a general statement for
an area such as Brisbane, which contains differing environments such as an urban canyon
and sprawling suburbs. This environmental distinction is exactly what the present project
investigated.
Air pollution and UV radiation
Studies have dealt with urban environments and air pollution and results support
the idea that pollution does attenuate UV a measurable, and possibly significant amount.
A study from Chicago, Illinois, USA, found that a negative relationship existed between
tropospheric ozone levels and UV radiation levels measured in the CBD [16]. Other
articles have reported similar findings relating to air pollution and its attenuating effect
on UV radiation in urban areas. A Taiwanese study found that the city of Taipei (which
is home to about 3 million people in the city proper – an area of approximately 270km2,
and about 6 million in the greater Taipei region) recorded many fewer days of high UV
index than other areas of the country (a small island of just under 36,000 km2) [17]. And
a Greek study [15], using data from meteorological sites in metropolitan areas (not
necessarily inside the urban canyon), found that approximately 40% of the total variance
in erythemal irradiance reaching the ground could be explained by variations in total
column ozone, and that a vary strong correlation existed between variations to UV at
305nm (within the vitamin D action range) and variations in total column ozone. When
UV was measured at these metropolitan sites correlation was also found between
variations in sulphur dioxide and variations in erythemal UV. To note however, the
measurements in this study were total column ozone and total column sulphur dioxide
44
(these are measurements of total atmospheric concentration of these particles, i.e. from
the Earth’s surface to the outer edge of the atmosphere) and not measurements of solely
tropospheric air pollution, so their relevance to the urban canyon is limited.
These previous works provided evidence that tall buildings and air pollution may
in fact reduce the amount of UV radiation, and in turn cutaneous vitamin D production
that occurs within the urban canyon. This project set out to rigorously test that theory.
45
3. Assessment of UV exposure
In order to better understand the impacts - both positive and negative - of human
exposure to UV radiation the measurement of ambient UV and of the health outcomes is
necessary. The following chapter describes the processes and instrumentation used
during such measurement.
3.1. Measurement of UV radiation
In order to determine the amount of UV radiation to which something is
subjected, it is customary to measure radiant exposure, which is defined as incident
energy per unit of surface area. Common units for this are Joules per square meter (Jm-2).
For measuring the irradiance (or the density of incident radiation), units of Watts per
square meter (Wm-2) are standard. If a narrow portion of the UV spectrum is being
studied, then Watts per square meter per nanometre are commonly used (Wm-2nm-1).
A large amount of the research into UV radiation has been conducted with the
intent of better understanding the different effects of exposure to humans, thus a unit that
is quantifiable in terms of human exposure was developed, this unit is the MED, or
‘Minimum Erythema Dose’. One MED is the amount of erythemal UV (or sunburning
UV radiation) that is needed to produce barely perceptible erythema (or sunburn) in
people of Fitzpatrick skin type I after an interval of 8 – 24 hours directly following UV
exposure. The Fitzpatrick skin type scale has been developed to categorize the colour
and reactions to UV exposure an individual’s skin experiences (table 2).
46
Fitzpatrick skin types [91]
Table 2: Description of Fitzpatrick skin types I-V
1 MED is normally associated with 200(Jm-2) - 300(Jm-2) [29, 91]. This is the most
commonly used unit for the measurement of the negative biological effects of UV,
however it can be cumbersome because skin types vary from person to person, and
therefore it is difficult to use for comparisons between different people. Recently a new
unit has been introduced – the Standard Erythemal Dose (SED). 1 SED is defined as
100(Jm-2) [92].
These different measurements can be difficult for the lay-person to understand,
however it is very important to be able to transmit to the general public an idea of the
amount of UV radiation present in their environment and in turn an idea of what methods
of protection they ought to employ in order to stay safe from the harmful effects of the
sun. For this reason the World Health Organization (WHO) devised the UV index. The
UV index is a scale that categorizes the danger of prolonged exposure to solar UV for a
given point in time. It is an increasing scale that starts at 0 with different danger levels
defined as follows: 0-2 low danger, 3-5 moderate danger, 6-7 high danger, 8-10 very high
danger, and 11+ extreme danger. The UV index is usually presented graphically in a
fashion similar to the following…
47
Figure 12: UV index developed by the WHO to aid with public understanding of UV danger [93]
The index can be used to show how much UV radiation a location received in the past,
the current UV conditions, or as a forecast for the future [93].
3.2. Electronic instrumentation Quantitative study of the electromagnetic spectrum is spectrophotometry, and a
spectrophotometer is an instrument used for studying the EM spectrum. These
instruments work by accepting light from the source being studied, separating out the
portion of the spectrum of interest from all other EM radiation, and finally quantifying
the amount of radiation available within the section of interest. Instruments vary in both
the manner in which they select the measured portion of the spectrum and the precision
with which they measure the radiation. Standard methods of selecting a portion of the
EM spectrum for study include the use of diffraction gratings, monochromators, and
filters, with each method being useful and appropriate for various measurement
circumstances.
A diffraction grating is a surface covered with a regular pattern of parallel lines
which has the ability to diffract incident EM radiation. Diffraction gratings are used
48
alone in CCD (charged coupled device) spectrometers or in combination with a series of
slits and mirrors as in a monochromator. CCD spectrometers pass incident radiation to a
diffraction grating and then onto a CCD array where energy recorded in a specific
location is associated with a specific wavelength of radiation. These instruments contain
no moving parts and are useful for field study or other similar situations where the
instrument must be portable and durable. An example of a CCD spectrophotometer can
be seen below.
Figure 13: CCD spectrometer - light/UV radiation enters from a detector connected at point (A), is separated into its constituent wavelengths by the diffraction grating (B), and is absorbed and passed to a
computer for analysis by the CCD array (located on opposite side of panel) (C)
A monochromator makes use of a diffraction grating along with additional slits
and mirrors in order to measure only a very small portion of the EM spectrum
(instruments vary in their precision, but measurement of 1nm bands is possible in high
quality models). A monochromator can be adjusted to measure different wavelengths by
moving one of the mirrors and a group of wavelengths can be measured by measuring
many single wavelengths in succession. Monochromators can be very precise
instruments, but are generally only for laboratory use as the moving parts and multiple
mirrors can easily fall out of alignment if the instrument is moved. A diagram of a
monochromator follows.
49
Figure 14: Light (A) is focused onto an entrance slit (B) and is collimated by a curved mirror (C). The collimated beam is diffracted from a rotate-able grating (D) and the dispersed beam re-focussed by a
second mirror (E) at the exit slit (F). Each wavelength of light is focussed to a different position at the slit, and the wavelength which is transmitted through the slit (G) depends on the rotation angle of the grating
The final method of selecting a portion of the spectrum for study is the use of a
filter. Many broadband detectors use filters to filter out all EM radiation outside of a
specific band. These detectors then quantify the incident energy within that band.
Figure 15: Filter only allows UV radiation to pass through
These instruments do not distinguish between different wavelengths within the
selected band, only measuring the total energy across the unfiltered band. Instruments of
50
this nature are less precise, but generally cheaper than the previously mentioned types.
They are typically portable as well.
Instruments of all three types were used during this project and are described
specifically in chapter 5.
3.3. Dosimetry
Dosimetry is a technique used to measure the amount of UV radiation received by
a person or at a specific location during a specific exposure period. During this project
an in-vitro model of vitamin D synthesis was used to measure the amount of UV
radiation available for vitamin D synthesis. An in-vitro process is one in which an
experiment is performed within a controlled environment outside of a living organism,
for example within a test tube. During this project in-vitro dosimetry was used to
measure vitamin D production and is described in detail in chapter 4.
51
4. Vitamin D dosimeter
4.1. Overview of the vitamin D dosimeter
As discussed in chapter 3, the production of vitamin D begins in the skin when
UVB radiation interacts with 7-dehydrocholesterol (7-DHC), which results in the creation
of cholecalciferol. The vitamin D dosimeter used during this study models this process.
The dosimeter is an in-vitro model that consists of a liquid solution containing 7-DHC
which is exposed to UV radiation. The result of this exposure is a reaction that produces
cholecalciferol. This solution is then analysed with the use of an HPLC (High
Performance Liquid Chromatography - described in section 4.2) system to determine the
amount of 7-DHC still remaining and the amount of cholecalciferol that has been
produced. In-vitro models of vitamin D synthesis have been used prior to this study and
have been shown to be effective for the measurement of the vitamin D production
capacity of sunlight [51, 94-98]. Sample preparation involves dissolving powdered 7-DHC (Sigma D4429-56
93.7% purity) in ethanol under lamps that do not emit energy in the UV range. Standard
procedure is to produce a quantity of solution large enough to be used during an entire
experiment so that all samples during a test have the same starting concentration of 7-
DHC. From this larger stock solution individual samples are pipetted into quartz cuvettes
for exposure. Quartz cuvettes are used instead of other materials because glass or plastic
attenuate UVB radiation. Quartz allows UVB to pass through and therefore makes the
production of vitamin D possible in this situation. A description of the cuvettes can be
found in section 6.1.
When a sample is exposed to UV in the 290-315nm range the same natural
process that occurs in the skin occurs in the solution, that is, the 9-10 carbon-carbon bond
in the B-ring of 7-DHC is broken. After subsequent thermo-isomerisation cholecalciferol
is produced. Just as with cholecalciferol in the skin, further exposure of the solution to
52
UV can lead to the production of tachysterol, lumisterol, and other photoproducts, as well
a reversion back to 7-DHC [51, 99].
Finally, an important property of this vitamin D dosimeter is that it provides the
possibility of taking standardized measurements of the vitamin D production capacity of
sunlight in different situations and at different times. This model strips away many of the
factors that can confound measurements of 25(OH)D taken from human blood such as
skin colour, and the amount of 7-DHC in an individual’s skin. When sample
concentration, duration of exposure, placement of cuvettes, stray UV radiation during
transport, and other experimental-setup and analysis variables are controlled for it is
possible to compare results obtained with this model in one situation to those measured in
other situations with a great deal of confidence. And while the amount of cholecalciferol
produced in a certain situation may not directly equate to that which a specific individual
might produce, the simplicity of the model makes it a more cost effective and less
resource intensive option for measurements of environmental conditions.
4.2. High Performance Liquid Chromatography (HPLC)
The in-vitro model used in this project has previously been employed by
Terenetskaya and Galkin [87, 88, 90, 91], but the use of HPLC as a method of sample
analysis was only done in one of these studies. The main reasons for this are cost and
availability of HPLC equipment. HPLC is considered to be the ‘gold standard’ for
analysis of this type, however a system is expensive and not many laboratories
investigating vitamin D production have them. ASHRL is fortunate enough however to
house a state-of-the-art system in its laboratory, and ASHRL’s system was put to use
analysing the samples collected during this study.
An HPLC analysis procedure consists of two parts, a mobile phase and a
stationary phase. The mobile phase is a solution that is continuously run through the
system into which a small volume of sample is injected. This sample passes through the
column (or stationary phase) in which a large number of very small particles are packed
53
into a narrow tube. HPLC separates the sample into its different constituent compounds
by making use of the chemical interactions between the stationary phase, the mobile
phase, and the different properties of the samples themselves. These interactions produce
a separation between the different compounds in each sample, with each compound
passing through the column at a different rate. Each compound then passes through the
detector (located just after the column), at a time specific to said compound and the
conditions inherent in the interactions between the mobile and stationary phases. The
detector functions by emitting UV or visible radiation at a determined wavelength and
measuring the changes in absorbance that occur as various parts of an injected sample
pass through the detection beam. The elution time is used to identify each unique
substance within a sample, while the concentration of a substance is determined by the
absorbance measured by the UV/Vis detector. The HPLC system in the ASHRL
laboratory is described in section 6.1.
4.3. Analysis of vitamin D samples
In relation to the HPLC analysis for this in-vitro model, there have been two
different isocratic mobile phases which have been proven to successfully separate
cholecalciferol, 7-DHC and the other photoproducts created when UV interacts with 7-
DHC. The first uses a methonal:ethanol:water (86:10:4) mixture and was adopted from
the work of Porter et al. [100], while the second uses a methonal:water (95:5) mixture
and was adopted from the work of Yamamoto and Borch [101]. The first of these is used
in the ASHRL laboratory and was put to work during this project. Chemicals used were
methanol (Sigma 34860 Chromasolv for HPLC) and ethanol (Sigma 270741 Chromasolv
for HPLC).
54
5. Project aims and research questions
Following on from the results of the preliminary investigation, the main portion of
this project was designed using an in-vitro vitamin D dosimeter to asses the association
between UV radiation and vitamin D production within the urban canyon. This project
aimed to quantify the differences between the urban canyon environment and the
suburban surroundings in terms of both ambient UV radiation and vitamin D production.
Study design and data collection were guided by the following research questions:
• Measured at similar times of day and under similar atmospheric conditions is
there consistently less total ambient UV available inside the Brisbane CBD than
in the surrounding suburban area?
• How does ambient UVA and UVB radiation vary over time in these distinct
locations?
• Over time is there a difference between the Brisbane CBD and suburban
surroundings in terms of the measured erythemal UV and measured
cholecalciferol production?
• Do air pollution, humidity, and temperature impact upon the amount of available
total UV radiation, erythemal UV radiation, and cholecalciferol production in the
Brisbane CBD and suburban surroundings?
These research questions were addressed by first conducting two pilot studies and
then a major study lasting approximately three months. The following chapters discuss
the methods, results and implications of these studies.
55
6. Methodology and Instrumentation
Observational measurement during this study consisted of the collection of
erythemal UV data, solar spectrum data, and in-vitro vitamin D production samples. In
addition, urban air pollution data, and environmental data were obtained from sources
that continuously monitor those phenomena. This chapter describes the instruments used
during data collection and their calibration. Table 3 shows a condensed list of the
instrumentation used.
56
Table of measurements collected during this study and the instrumentation used during data collection
Pilot study #1 – measurement of erythemally weighted UV at various urban canyon
locations and at a suburban site Measurements Instrumentation
Instantaneous and integrated erythemally-weighted UV at urban canyon locations
Portable photometer/radiometer (Solar Light Company model PMA2100) and
detector (Solar Light Company PMA2101) Instantaneous erythemally-weighted UV at
suburban site UV biometer (Solar Light company model
501)
Pilot study #2 – measurement of erythemally-weighted total UV and erythemally-weighted diffuse UV in the urban canyon and erythemally-weighted total UV at a
suburban siteMeasurements Instrumentation
Instantaneous and integrated erythemally-weighted total UV at urban canyon location
Portable photometer/radiometer (Solar Light Company model PMA2100) and
detector (Solar Light Company PMA2101) Instantaneous erythemally-weighted diffuse
UV at urban canyon location Portable photometer/radiometer (Solar
Light Company model PMA2100), detector (Solar Light Company PMA2101), and
occulting disc Instantaneous erythemally-weighted total
UV at suburban site UV biometer (Solar Light company model
501)
Main study – measurement of in-vitro vitamin D production, erythemal UV, UV spectrum, and air pollution at 5 urban canyon sites and 1 suburban location
Measurements Instrumentation In-vitro vitamin D production at all
locations Quartz cuvettes (Starna Ptd. Ltd. Product code: 21/Q/10), powdered 7-DHC (Sigma
D4429-56 93.7% purity), and ethanol (Sigma 270741 Chromasolv for HPLC)
Analysis of in-vitro vitamin D samples Shimadzu Prominence model LC-20A modular HPLC system
Instantaneous and integrated erythemally-weighted UV at all locations
Portable photometer/radiometer (Solar Light Company model PMA2100) and
detector (Solar Light Company PMA2101) UV spectrum at all locations Portable spectrometer (StellarNet model
epp2000) Air pollution Data obtained from Queensland EPA
Table 3: Description of measurements and instrumentation used during two pilot studies and the main project
57
6.1. Instrumentation used
Erythemal UV measurement
The instrument used to collect erythemal UV data was a portable
photometer/radiometer (Solar Light Company model PMA2100) that connects to a
detector (Solar Light Company PMA2101) that collects both instantaneous and integrated
MED information. This instrument is of the type that employs the use of a filter in order
to select the wavelengths for measurement (described in section 3.2). This filter is
erythemally-weighted and its construction and domed shape result in an angular response
very close to that of an ideal cosine function making it suitable for measurements of
direct and diffuse radiation [102].
Figure 16: Handheld PMA2100 control module that connects to erythemally-weighted detector PMA2101 UV detector.
This instrument’s instantaneous measurement function represents the amount of
erythemal UV that there is at a study site at any given point in time (for example: 2.56
MED/hour). The integrated measurement function represents the amount of erythemal
UV a site has received over a period of time that the operator specifies (for example: 0.85
MED during a twenty minute measurement). The instrument is capable of recording the
58
integrated UV measurement while at the same time displaying the instantaneous UV
reading, allowing the measurements to be recorded simultaneously.
In addition, a similarly functioning stationary photometer/radiometer (Solar Light
Company model 501) was used during preliminary studies. This instrument is located on
the roof of the ASHRL building at QUT’s Kelvin Grove campus.
Measurement of the solar spectrum
Measurement of the solar spectrum was accomplished with the use of a portable
spectrometer (StellarNet model epp2000), which contains a diffraction grating and CCD
array (described in section 3.2). This instrument measures across the UV and visible
portions of the spectrum and provides data describing the amount of radiation at different
wavelengths. It measures incident radiation in half-nanometre steps, and is coupled with
an input attachment that accounts for the cosine response properties of input radiation.
The instrument is powered by a small portable battery pack and connects to a laptop
computer for data acquisition. StellarNet software is used in conjunction with the
spectrometer during data collection and analysis.
Figure 17: Image of StellarNet battery pack (left) and epp2000 spectrometer (right)
This instrument has the capability to take measurements between 190nm and
1600nm, and the option to select a smaller portion of this range for analysis. Also the
59
option to vary the scan duration is available and the instrument boasts a linear response
curve over time, meaning that if necessary scans of different durations can be compared.
HPLC system
ASHRL’s HPLC system is a Shimadzu Prominence model LC-20A. This is a
state of the art modular system, that when combined with the correct column, has the
capability to perform rapid and accurate analysis of the photoproducts being dealt with
during this study. This system consists of the following modules: control module,
pump/de-gasser module, auto-sampler, column oven, UV-VIS detector, and fluorescence
detector.
• Control Module: Connects the other components to one another and to the
computer software.
• Pump/de-gasser Module: De-gasses each solvent being used and then mixes them
together in the correct quantities, creating the mobile-phase.
• Auto-sampler: Allows for the automated processing of multiple samples. An
injector unit selects samples from a rack (with capacity for up to 105 samples)
according to a pre-set schedule.
• Column Oven: Maintains a constant temperature around the column, thus
eliminating the effect that changing temperatures in the laboratory have on
retention time.
• Column: Silica based, non-polar, Phenomenex C-18 column.
• UV-VIS Detector: Analyses samples by releasing EM-radiation (190-700nm) and
measuring the amount of absorbance at the same wavelength. This system has the
capability to measure on two wavelengths simultaneously. This form of
detection has been used before for analysis with the in-vitro model of vitamin D
synthesis.
• Fluorescence Detector: Releases EM-radiation at a specified wavelength (200-
650nm) and observes on a different wavelength. This form of measurement has
60
not been used along with the in-vitro model previously. The fluorescence detector
was not used during analysis of samples during this study, but is mentioned
because it is attached to the other modules. An image of the system is shown
below.
Figure 18: ASHRL's HPLC system - 1) pump/de-gasser 2) control module 3) auto-sampler 4) column oven 5) UV/Vis detector 6) fluorescence detector
In-vitro model of vitamin D synthesis
During exposure of vitamin D in-vitro model samples quartz cuvettes (Starna Ptd.
Ltd. Product code: 21/Q/10) were used. Quartz cuvettes were employed because it has
been shown that both plastic and glass attenuate UV radiation. The cuvettes used in this
study have been rated to allow UV above the wavelength of 170nm to pass through and
are therefore acceptable for the purposes of this in-vitro model [96].
61
Figure 19: Image of the four quartz cuvettes used during this study
These cuvettes have a capacity of 4mL. Four cuvettes were available for use during this
project, and therefore four samples were exposed at each location.
During this study a solution of approximately 300μg/mL was used for all
exposures. This concentration was chosen after preliminary tests showed 300μg/mL of 7-
DHC to produce a response that is approximately 75% of the HPLC detector’s upper
limit. This concentration was shown to produce detectable amounts of cholecalciferol
during laboratory tests conducted in a range of UV conditions from 0.25 to 3.00 MED.
This was ideal because it provided measurable results during relatively low UV
situations, but also did not produce concentrations beyond the detector’s scale during
high UV periods. Figures 20 and 21 show the results of a test that exposed different
samples of the vitamin D dosimeter (all 300μg/mL) to different amounts of UV radiation
and the subsequent cholecalciferol that was produced.
62
Figure 20: Results of the analysis of 7 samples of exposed 7-DHC and the resultant presence of cholecalciferol and other photoproducts.
Figure 21: Enlargement of figure 20 showing relationship between amount of UV exposure and amount of cholecalciferol production.
In viewing figures 20 and 21 there are two important things to note: (1) The very
consistent elution time of both compounds. The elution time is represented by the time at
63
which the peak presents (scale on the bottom of the image is time in minutes). The
elution time is used to identify each compound. (2) The relationship between increasing
exposure and increasing production of cholecalciferol. This relationship is represented
by the decrease in 7-DHC concentration and corresponding increase in cholecalciferol
concentration associated with increasing exposure (exposures are labelled in the order of
their corresponding line on the graph). It can be seen that 0.25MED (the lowest
exposure) resulted in the least amount of cholecalciferol produced and the greatest
amount of 7-DHC remaining after exposure, and that 3MED (the greatest exposure)
resulted in the greatest amount of cholecalciferol produced and the least amount of 7-
DHC remaining after exposure. This shows that the model functions as described, UV
radiation is converting 7-DHC into cholecalciferol. Other photoproducts are also created,
which can be seen on the left side of figure 20.
During analysis of exposed samples the UV/Vis detector’s dual wavelength
analysis capability was put to use. Pre-project tests determined that the highest output
signal for detecting 7-DHC was obtained at a detector wavelength of 281nm, and that the
highest output for cholecalciferol was obtained using a wavelength of 266nm. These
respective wavelengths were used for detection during this project. Examples of the
output after the analysis of two samples are shown in figures 22 and 23.
64
Figure 22: Laboratory solution of 7-DHC and cholecalciferol that was un-exposed (cholecalciferol peak is large in this un-exposed sample because it is a mixture of chemical standards of both 7-DHC and
cholecalciferol and a large amount was added to the solution)
Figure 23: Comparison between an unexposed sample of 7-DHC in ethanol and an exposed sample of 7-DHC in ethanol (view is of detector output at 281nm - optimised for detection of 7-DHC)
The first image shows a solution of only 7-DHC and cholecalciferol that was produced
in the laboratory using chemical standards and not exposed to UV radiation, while the
65
second shows a solution of only 7-DHC that was produced in the laboratory and then
exposed outdoors. One can see that the elution times of the different samples are the
same, meaning that the analysis parameters were consistent between samples. Impurities
are present in even the chemical standards and can be seen in the first image. The second
image shows one exposed sample and its associated control, and from this image it is
easy to see the large decrease in 7-DHC due to UV exposure. Also visible is the increase
in cholecalciferol and other photoproducts that result from the breakdown of the 7-DHC
(anywhere the blue line is higher than the pink line this is the case).
Pollution monitoring
The Queensland Government’s Environmental Protection Agency (EPA) runs a
network of pollution monitoring stations in the southeast portion of Queensland. One of
these monitoring stations is set up near the Brisbane CBD. The site is situated atop a
building at the QUT Gardens Point campus, which is located on the edge of the CBD.
This station has the capability to measure visibility-reducing particles (measured as
visibility loss due to haze) and PM-10 sized particles (particles less than 10 microns in
diameter measured in μg/m3). Visibility-reducing particles are measured using an
integrating nephelometer, while PM-10 particles are measured with the use of a tapered
element oscillating microbalance. These instruments are maintained and calibrated by
EPA/QUT staff and data is made available to the public over the internet.
Environmental conditions
This data was obtained from a weather station (Davis Instruments, Vantage Pro2)
located on the roof of the ASHRL building near the suburban data collection location.
From this weather station both temperature and humidity data was collected. Data at this
site is collected once per minute throughout the day. This weather station is maintained
and calibrated by ASHRL research staff.
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6.2. Calibration of instruments
During data collection all instruments were calibrated regularly so as to ensure the
quality and accuracy of results. The following is a discussion of the procedures followed
during the calibration of each instrument.
Erythemal UV detector – Solar Light Company model PMA2100
The handheld erythemal UV detector was calibrated against an erythemal UV
detector (Solar Light Company UV-Biometer 501) that is located on the roof of the
ASHRL laboratory. This instrument is factory calibrated and is used as the laboratory
standard. During calibration the handheld PMA2100 was taken to the laboratory roof and
placed three meters from the (UV-Biometer 501). Data was recorded from each
instrument every ten minutes between 9:00am and 12:00pm. From these measurements a
correction factor was determined and added to the data recorded with the PMA2100
during data collection.
CCD Spectrophotometer – StellarNet epp2000
The portable CCD spectrophotometer was calibrated using the ASHRL secondary
standard (Optronics Laboratories Lamp F-789) calibration lamp. This lamp is regularly
calibrated against the ASHRL primary standard NIST (National Institute of Standards
and Technology) standard (Optronics Laboratories Standard of Spectral Irradiance FEL-
788) lamp in the ASHRL laboratory and used for calibrating other instruments. During
calibration between the primary and secondary lamps a spectrophotometer (Acton
Research SpectraPro 2300i Imaging Triple Grating Monochromator) with a diffraction
grating and monochromator was used. The primary standard lamp has a known
irradiance at a distance of 50cm and is considered to be of the highest quality. The
67
irradiance of the secondary standard was determined during a calibration at 50cm
between these two lamps.
The secondary lamp was then used to calibrate the epp2000. During this
procedure the secondary lamp was run at a distance of 50cm from the epp2000’s input.
From the counts recorded during this procedure by the epp2000 and the known irradiance
of the secondary lamp a value of irradiance per count was determined for each
wavelength measured by the epp2000. During data collection with the epp2000 a dark
scan was taken in order to zero the epp2000 instrument before each use.
HPLC
In order to calibrate the HPLC system a calibration curve was created using high
quality 7-DHC and cholecalciferol standards. A calibration curve is used to determine
the concentration of a substance in an unknown sample by comparing the unknown to a
set of standard samples of known concentration. Five samples of different known
concentrations were made up using chemical standards for cholecalciferol (Sigma C9756-
1G 98% purity) and 7-DHC (Sigma D4429-56, 93.7% purity). Concentrations used
were: 2μg/mL - 12μg/mL for cholecalciferol and 25μg/mL - 350μg/mL for 7-DHC,
which covered the range of experimental results. Each of these samples was run through
the system under the same conditions and in the same manner as all of the exposed
samples. The detector reading for each sample was associated with the respective known
sample concentration, resulting in a linear relationship between detector counts and
sample concentration for each compound. The linear relationships derived were then
used to determine the concentrations of samples exposed during the collection of
observational measurements using the in-vitro model of vitamin D synthesis. The
calibration curves produced during this project were associated with a high degree of
precision. The average R-squared values for linear calibration curves for 7-DHC and
cholecalciferol were respectively: 0.9993 and 0.9991. Calibration of the HPLC system
took place each time the mobile phase was changed, because any change to the mobile
could slightly alter the separation occurring during sample analysis.
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7. Pilot study Two significant projects were completed prior to the initiation of the main study.
These projects were conducted in Brisbane’s CBD and provided a basis for the work that
followed. The first was an investigation into the difference between UV levels measured
in the urban canyon and those measured at a nearby suburban site. This study was
similar in nature to that preformed in Lodz, Poland by Podstawczynska and Pawlak [2],
but was conducted in an area with buildings of significantly greater height. The second
was a comparison between levels of total UV and diffuse UV within the CBD. This was
conducted at a location in which there was a direct view of the sun all day long (study site
5, Post Office Square, discussed in section 8.3).
The results of these studies show that there is a significant difference between the
amount of erythemal UV measured at street level in the urban canyon and the amount of
erythemal UV measured at a nearby suburban location. In addition, this work showed
that diffuse UV had a large and variable impact on the amount of UV in the urban
canyon.
7.1. Project one
Study of UV in urban canyon vs. UV at suburban site
Study Goals
The goal of this study was to measure UV radiation at various sites in the urban
canyon while simultaneously measuring UV at a suburban location in order to investigate
the effect that the urban canyon has on UV attenuation. MED data was collected at five
locations in Brisbane’s CBD – the same sites described in section 8.3. Data collected in
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the CBD was compared to data collected on the same days with ASHRL’s roof mounted
detector (described in section 6.1) , which is located 2.5 kilometres outside Brisbane’s
CBD, and also to guidelines for exposure times determined in a recent study published in
the Medical Journal of Australia - “Estimates of beneficial and harmful sun exposure
times during the year for major Australian population centres” [4]. This study used
previously collected UV data to calculate healthy exposure times for each month of the
year in major Australian population centres.
Atmospheric conditions and data collection
The atmospheric conditions were clear and sunny during data collection. Data
was collected using the photometer/radiometer (Solar Light Company model PMA2100).
Data collection began at 9:00am and continued by rotating between sites until 3:30pm.
Data was collected continuously for ten minutes (instantaneous MED being recorded at 0,
5 and 10 minutes and integrated MED being recorded at 5 and 10 minutes) at each site
during rotation except during the lunch hour. During this mid-day period data was
collected in the public square continuously for 30 minutes from 1:31pm – 2:01pm. The
data collected in the CBD was compared to data collected every five minutes throughout
the day on the roof of the building in which the ASHRL laboratory is located using a
stationary UV biometer (Solar Light company model 501).
Results and discussion
The most significant factor determining the instantaneous amount of MED
received at any given time was the availability of direct sunlight. When the CBD
detector was situated in direct sunlight the amount of erythemal UV received was
drastically greater than that received when only diffuse sunlight was present (Table 4),
however it still did not reach the level of erythemal UV measured at the ASHRL site.
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An example of the difference between the CBD and the ASHRL sites is as
follows: in direct sunlight at 12:00pm, the amount of instantaneous erythemal UV
measured in the public square was 1.826 MED/Hour, while the ASHRL site measured
2.676 MED/Hour at 12:00pm, which is 46.5% greater than that measured in the CBD.
Erythemal UV received during direct sunlight situations, versus that
received when only diffuse sunlight was present - Brisbane CBD.
MED/hour Location Time
Daily Max. 2.01 Post Office Square 12:01
Daily Min. 0.14 Creek Street (Site 2) 9:50
Average of Direct Sunlight Situations 1.37 Various (Brisbane CBD) 9am - 3:30pm
Average of Diffuse Sunlight Situations 0.32
Various (Brisbane CBD)
9am - 3:30pm
Difference Between Average UV in Direct and Diffuse situations
01.05
Various (Brisbane CBD)
9am - 3:30pm
Average Diffuse UV as a Percentage of Average Direct UV
23%
Various (Brisbane CBD)
9am - 3:30pm
Table 4: Results from the first pilot study
In all cases (direct and diffuse sunlight) the amount of erythemal UV received in
the urban canyon was significantly less than that received at the ASHRL monitoring
station. From this we can deduce that there were other factors in the environment (most
likely tropospheric air pollution) that had an attenuating effect on the UV radiation
reaching the bottom of the urban canyon.
The instantaneous amount of UV radiation received at each site can be seen in the
following charts, along with a comparison of data collected in the CBD and data
collected at the ASHRL site.
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Figure 24: Comparison of erythemal UV measured at various Brisbane CBD locations and the ASHRL monitoring station
This chart shows that the amount of instantaneous erythemal UV radiation received at the
CBD locations varies throughout the day, but that it never reached the level observed at
the nearby ASHRL site. It can also bee seen that the level of UV measured at different
sites within the CBD varies greatly from location to location even when measurements
are taken with relative temporal proximity.
In respect to vitamin D production we note the guidelines published in the article
mentioned previously [4], which presents exposure times for acquiring amounts of
vitamin D equal to recommended intakes in Australia. When this theoretical data is
compared with the empirical results of our study it does not correlate well with the data
collected in the CBD. The article recommends that for August, in Brisbane, at noon, 4 –
9 minutes of exposure are sufficient for vitamin D production (defined as a person of
Fitzpatrick skin type II receiving 1/3 to 1/6 of an MED with 15% of their body exposed),
and that this same exposure for 23 minutes would result in 1 MED. Comparing that to
the data we have at times near 12:00pm we find that none of the sites in the CBD
received UV radiation levels this high, but that the ASHRL site did. This trend holds for
Site Comparison - Instantaneous UV
0
0.5
1
1.5
2
2.5
3
7:00 8:30 10:00 11:30 13:00 14:30 16:00
Time of Day
M E D / H o u r
Post OfficeSqr. (Site 5)
Creek St.(Site 1)
Creek St.(Site 2)
Queen St. (Site 3)
Queen St. (Site 4)
ASHRL
72
the other times of day that the recommendations state as well. Below, table 5 presents the
comparison between the recommendations and the findings of this study.
Predicted Sun Exposure Times Compared to Measured Values
Values predicted by article, “Estimates of beneficial and harmful sun exposure times during the year for major Australian population centres” given in italics and values measured during this study given below.
Listed is the measured value for each site taken at the time nearest to the time of the predicted value.
Time Exposure Required to Receive 1/6 MED
(Min)
Exposure Required to Receive 1/3 MED
(Min)
Exposure Required to Receive 1 MED
(Min)
10:00
Prediction 10:00 6 NA 32*
Site 1 9:35 46.96 93.92 281.77
Site 2 9:58 67.33 134.67 404.01
Site 3 10:06 31.80 63.59 190.78
Site 4 10:21 36.48 72.97 218.90
Site 5 9:10 33.30 66.60 199.80
ASHRL 10:00 5.79 11.57 34.72
12:00
Prediction 12:00 4 9 23
Site 1 12:11 7.14 14.28 42.83
Site 2 12:26 51.74 103.47 310.42
Site 3 11:25 22.56 45.11 135.33
Site 4 11:40 5.38 10.77 32.30
Site 5 12:00 5.02 10.03 30.09
ASHRL 12:00 3.74 7.47 22.42
Table continued on next page…
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15:00
Prediction 15:00 NA 29 32*
Site 1 14:21 40.70 81.40 244.20
Site 2 14:38 28.44 56.88 170.64
Site 3 14:55 51.45 102.89 308.68
Site 4 15:00 63.59 127.19 381.56
Site 5 15:17 29.26 58.51 175.54
ASHRL 15:00 12.26 24.51 73.53
* This value is “the least amount of exposure time to produce 1 MED (or erythema) based on the maximal Ultraviolet Index (UVI) reading for that month either at 10:00 or 15:00”. Values were not given for 1/3
MED at 10:00 or 1/6 MED at 15:00
Table 5: Comparison between measured values and predicted values
As seen in table 5, the measured times required to receive either 1/6MED or 1/3MED in
the urban canyon were significantly greater than those predicted in this study (predicted
from data collected outside of the urban canyon). It demonstrates that the urban canyon
may indeed limit the amount of erythemal UV that reaches ground level.
It is very important to note that, although measuring erythemal UV is the most
common method used to measure UV radiation in terms of human health outcomes, it
does not directly measure the amount of vitamin D-producing UV present in a given
situation. Along with the fact that erythemal UV was measured in this work and the
comparison study, the pollution present in the environment was not measured. For this
reason no statement can be made regarding pollution except to say that it is assumed that
attenuation due to air pollution was a factor in the reduction of UV measured in the urban
canyon, especially at site 5 (Post Office Square) where there was a wide sky view and
direct view of the sun.
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Conclusions
This study has found evidence to support the theory that, at times, highly
urbanized environments may significantly diminish the amount of UV radiation reaching
street level when compared to nearby less-urbanized areas. It was found that
measurements of erythemally-weighted UV radiation collected at 5 sites in the urban
canyon were significantly lower than similar measurements collected at the same times in
a nearby non-urban canyon location. In addition, measurements were significantly lower
than values predicted by a recently published study. The consequences of this are that
recommended exposure times created at sites in nearby suburban areas may not provide
accurate information for people spending their time in the urban canyon.
7.2. Project two
Study of total UV vs. diffuse UV in the urban canyon
Study goals
The goal of this study was to simultaneously measure total erythemal UV and
diffuse erythemal UV at a single site in the urban canyon in order to investigate the
relationship between diffuse and total UV throughout the day. Diffuse UV is that which
is scattered during its travel from the sun to an observer. Both total MED data and
diffuse MED data were collected in Post Office Square during a single day. This site has
an unobstructed view of the sun all day long.
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Atmospheric conditions and data collection
The atmospheric conditions were clear and sunny all day long. Data was
collected using the photometer/radiometer (Solar Light Company model PMA2100). The
diffuse measurements were achieved through the use of an occulting disc. This disc was
used to cast a shadow over the erythemal UV detector which blocked direct UV from
reaching the sensor. The occulting disc was held at such a distance that its shadow only
just covered the detector, thus blocking direct UV, but allowing all diffuse UV to the
detector. Data collection began at 11:15am and continued until 3:00pm. Instantaneous
MED data for both total UV and diffuse UV was recorded each five minutes. Integrated
MED data for total UV was recorded every five minutes. Integrated diffuse UV was not
recorded because the occulting disc was only momentarily placed between the sun and
the detector once every five minutes in order to take an instantaneous diffuse UV
measurement.
For comparison with a nearby suburban site, total UV data was again collected
every five minutes throughout the day using the UV biometer (Solar Light company
model 501) situated on top of the ASHRL laboratory, located outside of the CBD and 2.5
km away from the study area.
Results
When instantaneous total UV was compared to instantaneous diffuse UV it was
found that throughout the measurement period the level of diffuse UV stayed relatively
constant, whereas the level of total UV varied a great deal (this can be seen in the
following chart). Around noon, total UV levels were greater than 4 MED/hour, while at
3:00pm total UV levels had dropped to below 2 MED/hour. Diffuse UV levels remained
relatively constant at approximately 0.75 – 1 MED/hour (lowest levels being found later
in the day), which means that near noon, when total UV was highest, diffuse UV made up
only approximately 24% of total UV, but that at 3:00pm, when total UV was
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approximately 2 MED/hour, diffuse UV made up nearly 40%. The following chart
shows these relationships.
Figure 25: Along with these results, it was also found that total UV measured at the ASHRL site was in fact significantly greater than that measured in the urban canyon.
As the sun passed through the sky the solar zenith angle changed continuously and levels
of UV reflect this. The SZA was smallest around noon (peak of the graph) and increased
until the end of collection.
An interesting event occurred between 1:30 and 2:00pm when the sun moved into
a position in which it reflected directly off of the window of a nearby building,
effectively enhancing both measured levels of total UV and diffuse UV. The effect
created was such, that there were two separate directions from which intense UV was
coming, the first directly from the sun, and the second directly from the office window.
This event can be seen in the group of four points between 1:30 and 2:00pm that do not
directly follow the trend of the rest of the data set. As with the first project, the level of
erythemal UV measured in the urban canyon never reached the level measured at the
ASHRL site.
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Limitations
It is very important to note that, as with the previous study, this also was
conducted using measurements of erythemal UV, and cannot be taken as a direct measure
of vitamin D production capability. The pollution present in the environment was not
measured, and therefore no statement can be made regarding pollution except to say that
it is assumed that attenuation due to air pollution was a significant factor in the reduced
amount of UV measured in the urban canyon when compared to the ASHRL site.
Conclusions
This study again found evidence to support the theory that, at times, highly
urbanized environments may significantly diminish the amount of UV radiation reaching
street level when compared to nearby less-urbanized areas. Often times the only UV
available inside the urban canyon is diffuse UV, and this study has shown that it is
possible for the difference between total and diffuse UV in the urban canyon to be
substantial during the middle of the day. Also, it was shown that at this site, that
although the level of total UV varied greatly throughout the day, there was more or less a
constant level of diffuse background radiation.
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8. Main study: Investigation of erythemal UV exposure and vitamin D production in the urban canyon
8.1. Study outline The aim of this project was to better understand human UV exposure in urban
environments and specifically to address the research questions discussed in chapter 5. In
order to do this a number of observational measurements were taken within the
downtown area of Brisbane, Australia during the winter of 2007. Emphasis was placed
upon the dual nature of UV exposure: erythema and skin cancer versus vitamin D
production, and how this specific environment affects the relationship between these
exposure outcomes. A group of study locations within Brisbane’s CBD and a nearby
suburban location were selected as data collection sites and measurements of the
available solar spectrum, erythemal UV radiation, and in-vitro vitamin D production were
collected. In addition, measurements of tropospheric air pollution, air temperature, and
humidity were obtained from monitoring stations located near the selected study sites.
Data collected at these various sites was then compiled and entered into SPSS software
for analysis.
8.2. Site selection criteria
Overview
Observational measurements for this study were collected within the CBD and
nearby suburban surroundings of Brisbane, Australia (27°S, 153°E). The Brisbane
metropolitan area is home to approximately 1.7 million people and contains a CBD
surrounded by a very large suburban area. Brisbane’s CBD models the inner city centres
79
of other large cities around the world as it boasts a number of skyscrapers and other tall
buildings and is subject to high levels of automobile traffic. The CBD is located on the
edge of the Brisbane River, which forms 2 sides (the Brisbane river curves as it passes
the CBD) of a triangular area of approximately 2 Km2 within which lies the urban
canyon. Figure 26 shows a map of the area.
Figure 26: Map of Brisbane CBD, the suburban site is approximately 2km from the CBD [103]
Within the space of the CBD are a myriad of different micro environments including:
clusters of skyscrapers, open public squares, narrow ally ways, an expressway, a long
river walk, a large number of apartment buildings, etc… In short, a very dynamic
environment within which live and work a large portion of Brisbane’s population.
Within this area five study sites were selected and used for data collection during the
project. Data was also collected at one suburban location, shown above as well.
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Measurements collected within the CBD were compared to those obtained at the
suburban site.
CBD site selection criteria
Four of the five locations within the CBD were located in close proximity to a
single intersection set squarely within the CBD. The fifth site was in a nearby public
open space, also within the urban canyon. The selection of the data collection locations
was based upon the following criteria…
Description of site selection criteria:
• CBD: Each site was to be located squarely within the CBD and not in the
transitional area between suburban and urban settings.
• Buildings: As per the previously described definition of an urban canyon (see
section 2.6), each study site was to be located along a street with at least 50% of
each side bordered by buildings of no less than 5 stories and no more than 30% of
each side of the street is bordered by building of 2 stories or fewer.
• An area of high foot traffic: As this study focused on better understanding human
exposure to UV it was desirable to collect data in areas in which people were
being exposed to UV.
• An intersection of two streets that fit the description of an urban canyon: As with
most large urban areas Brisbane’s streets are set up in the form of a grid, with
streets running perpendicular to one another. As the sun traverses its path across
the sky light falls in very different ways on the streets running in one direction
(Northeast/Southwest) as compared to streets running in the other
(Northwest/Southeast). Therefore, in order to thoroughly evaluate how the urban
environment affects UV exposure it was necessary to select sites running along
both of the grid axes. Having the sites located around a single intersection
81
allowed for data to be collected at multiple sites in this area within a short time
period.
• Location for data collection halfway down each side of each street: Having sites
on either side of the same street allowed for possible differences between sites
that were located very near to one another (for instance, the possibility that one
side of the street is in direct sunlight while the other is in the shade).
• Suitable locations for data collection: A practical requirement for each respective
site was the availability of a location in which data collection was possible and
representative of the general area. As measurements were taken in a dynamic and
ever changing environment it was necessary to select site in which foot and
automobile traffic would disrupt the collection process as little as possible. Along
with these considerations, attempts were also made to collect data in locations
where small shade structures (awnings or planted trees for example) would not
influence UV levels to a great extent.
• A location that had an urban open space nearby: Due to the height of buildings,
direct sunlight frequently does not reach street level. A site that did receive as
much direct sunlight as possible was desired for purposes of comparison between
both the other urban sites and the suburban site. In addition, many people seek
out locations of this nature during lunch breaks and other times of the day, thus
data collection in a site of this nature was desirable.
Summary of site selection criteria
• Not on the boundary between the CBD and the suburban area
• An intersection of two streets that each met the urban canyon criteria
• Within an area of high foot traffic
• Suitable locations for data collection on both sides, halfway down each street
• A nearby public open space
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The selection of the open space was based upon its proximity to the first four sites
and its popularity as a gathering spot for people during their breaks from work. In
addition to the four principal sites and the open space, data was collected at a
suburban location. The suburban site was selected for use as comparison with the
various CBD locations. A detailed description of the chosen sites follows in section
8.3.
8.3. Description of selected sites
Urban sites
The intersection of Queen and Wharf streets was selected as the focal point for
data collection during this study. Two data collection locations were located halfway
down Wharf Street and two more were located halfway along Queen Street from this
intersection. Along with the four locations near this intersection the urban open space
used was Post Office Square, which is approximately one and a half blocks down Queen
Street from the aforementioned intersection. An in-depth description along with images
of each site follows.
83
Figure 27: Map of Brisbane CBD showing the location of the five CBD data collection locations [103]
Figure 28: View down Wharf Street (left) and Queen Street (right)
84
Site 1:
Location: Wharf Street, Northeast side
Street direction: Northwest/Southeast
Street length: 90m
Street width: 12m
Average building height on this side of street: 42 stories
Percentage of skyview blocked by buildings: 14%
Sidewalk width: 3.75m
Percentage of sidewalk with overhead awning: 54%
Number of trees on sidewalk: 6
Data collection: Data collection occurred on the sidewalk approximately halfway up
Wharf Street. Direct sunlight was never present during the morning, as it was blocked by
the nearest building, although sunlight was often seen coming between the two buildings
on this side of the street and illuminating site 2. During noon and afternoon data
collection direct sunlight was encountered at various times as the sun passed the tops of
buildings to the north and west. These solar sightings were variable because there were
many buildings that had the ability to block the sun and it was only visible as it passed
between two of these. A small awning was connected to the building behind the site,
however this was narrow compared to the width of the sidewalk and did not hang over
the detection equipment. Vehicles did not stop near this site for any reasons other than
waiting for lights to change if traffic was backed up.
Figure 29: Site 1 as seen from across the street (left) and the sky-view from site 1 (right)
85
Site 2:
Location: Wharf Street, Southwest side
Street direction: Northwest/Southeast
Street length: 90m
Street width: 12m
Average building height on this side of street: 9.25 stories
Percentage of skyview blocked by buildings: 24%
Sidewalk width: 3.33m
Percentage of sidewalk with overhead awning: 52%
Number of trees on sidewalk: 4
Data collection: Data collection occurred on the sidewalk approximately halfway up
Wharf Street. Direct sunlight was often present during morning data collection for
fleeting moments as the sun passed a gap between the buildings directly across the street.
During noon and afternoon data collection direct sunlight was encountered at various
times as the sun passed the tops of buildings to the north and west. As time passed and
the sun rose higher the amount of direct sunlight increased during noon and afternoon
data collection. Occasionally delivery vehicles would stop near the site for short periods
of time.
Figure 30: Site 2 as seen from across the street (left) and the sky-view from site 2 (right)
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Site 3:
Location: Queen Street, Southeast side
Street direction: Northeast/Southwest
Street length: 200m
Street width: 14m
Average building height on this side of street: 11.7 stories
Percentage of skyview blocked by buildings: 7%
Sidewalk width: 4m
Percentage of sidewalk with overhead awning: 87%
Number of trees on sidewalk: 6
Data collection: Data collection occurred on a small island near the crosswalk halfway up
the street. Out of all the collection sites, this saw the least direct sunlight. The buildings
were situated in such a way that the only time in which it was possible to receive direct
sunlight was in the morning, but for the majority of data collection buildings beyond the
intersection of Queen and Wharf blocked this morning sun as well. A delivery zone that
was used frequently was located about five metres up the street from this location.
Figure 31: View of site 3 from across the street (left) and sky-view from site 3 (right)
87
Site 4:
Location: Queen Street, Northwest side
Street direction: Northeast/Southwest
Street length: 200m
Street width: 14m
Average building height on this side of street: 14.9 stories
Percentage of skyview blocked by buildings: 25%
Sidewalk width: 4m
Percentage of sidewalk with overhead awning: 52%
Number of trees on sidewalk: 12
Data collection: Data collection occurred on a small island near the crosswalk halfway up
the street. The situation was similar to site 3. Morning sunlight occurred infrequently
due to the same buildings blocking site 3. During the noon and afternoon collections it
was possible for this site to receive direct sunlight as the sun passed over some shorter
buildings across the street. This direct exposure was of short duration however, as the
sun would quickly pass back behind taller buildings. A bus stop was located about five
metres up the street from this location and occasionally buses would leave their engines
running while waiting to continue their route for five minutes or so.
Figure 32: View of site 4 as seen from across the street (left) and the sky-view from site 4 (right)
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Site 5:
Location: Post Office Square
Central green length: 92.5m
Central green width: 26m
Area of open space: 2405m2
Average surrounding building height: 26.5 stories
Percentage of skyview blocked by buildings: 40%
Outside path width: 4.5m
Number of trees on each side of green: 6
Data collection: This site was located near the centre of the public square and was open
to direct sunlight at nearly all times. During the morning, sun came through a gap
between the large buildings bordering the square and during the noon and afternoon
collections the open end of the square made the sun fully available. This location was
frequented by a great deal of people during the noon and afternoon collections, most of
whom were eating lunch. The number of people was estimated at between one and two
hundred at any given time, however it was very difficult to count as many were moving
about and people continuously entered and left the square. Many of these people chose to
sit in areas not shaded by trees; some wore hats and other sun protection, while others
made efforts to expose themselves to the sun.
Figure 33: View of Post Office Square, site 5, (left) and sky-view from data collection location in the centre of the square (right)
89
Suburban site:
Location: Athletic field at QUT Kelvin Grove campus
Percentage of skyview blocked by buildings: 0%
The suburban/control site was located in the athletic field on the Kelvin Grove
campus of QUT. This site is a large grassy area that is in full view of the sun from early
morning until late afternoon and is easily accessible from the ASHRL laboratory. Trees
border the field, but they are a good distance away from the middle of the field. There
were no objects that obstructed the view of the sun.
Figure 34: View of the suburban data collection site, the athletic field at the QUT Kelvin Grove campus
8.4. Collection of observational data
Sample collection schedule
Observational measurements were taken between June 22, 2007 and August 30,
2007. Data was collected at the six urban canyon sites following a rotating schedule of
two sites per day (sites 1 and 3 together, or sites 2 and 4 together), three times a day
(9am, 12pm, and 3pm), three days per week (Monday, Wednesday, and Friday). Data
90
was collected at the control site at the same times (9am, 12pm, and 3pm) twice a week on
Tuesday and Thursday. Samples of vitamin D were analysed the day following sample
exposure: Tuesday, Thursday, and Saturday for samples obtained in the CBD, and
Wednesday and Friday for control samples.
Data collection took place whenever possible; however it was cancelled on
various days due to rain (the sensitive nature of the electronic UV detectors would not
allow for exposure to water) and due to works to the ASHRL laboratory (improvements
being made that would not allow for use of the HPLC instruments). A general schedule
of activities for a day of data collection in the CBD is shown below.
Schedule for data collection days in the CBD
7:20am Mix stock solution of 300 μg/ml 7-DHC in ethanol, pre-label storage containers for
exposed solution
8:00 Leave for CBD
8:40 Begin data collection at first site of day
9:00 Finish data collection and travel to second site of day
9:10 Begin data collection at second site of day
9:30 Finish data collection
9:40 Return to ASHRL laboratory with exposed samples
10:20 Place exposed samples in heating unit
11:00 Leave for CBD
11:40 Begin second data collection at first site of day
12:00pm Finish data collection and travel to second site of day
Schedule continues on next page…
91
12:10 Begin second data collection at second site of day
12:30 Finish data collection
12:40 Return to ASHRL laboratory with exposed samples
1:20 Place exposed samples in heating unit
2:00 Leave for CBD
2:40 Begin third data collection at first site of day
3:00 Finish data collection and travel to second site of day
3:10 Begin third data collection at second site of day
3:30 Finish data collection
3:40 Return to ASHRL laboratory with exposed samples
4:00 Place exposed samples in heating unit
Sample collection procedure
At the beginning of data collection the cuvettes containing vitamin D dosimeter
samples were set out for exposure and the erythemal UV detector was positioned in close
proximity to these samples. Data collection with the erythemal UV collector began at the
same time that the vitamin D dosimeter samples were set out for exposure. Instantaneous
UV was recorded on the data collection sheet at the start of collection and every five
minutes thereafter for twenty minutes. Measurements of integrated UV were recorded at
the same intervals beginning at the five-minute mark. Data collection finished at the
twenty-minute mark and coincided with the end of exposure of the in-vitro vitamin D
samples.
92
During exposure of vitamin D samples and the collection of erythemal UV data
the CCD spectrometer and computer were set up and one scan of the total UV spectrum
was collected. Data was collected by holding the detector vertically, above head height,
near the location in which the vitamin D dosimeter samples were undergoing exposure
and the erythemal UV was being collected. The collection of this data occurred near the
mid point of the twenty-minute period of vitamin D dosimeter sample exposure. The
amount of available UV varied due to time of day, collection site, and weather conditions
and due to these variations it was necessary to vary the duration of data collection with
the CCD spectrometer in order to acquire a useful amount of data at some locations and
in order to not exceed the upper limits of the detectors capabilities at other locations.
Laboratory tests have shown the detector to have a linear response relationship in regards
to scan duration versus measured radiation, and the different scan durations were
accounted for during data analysis.
In-vitro model of vitamin D synthesis
From a stock solution of 7-DHC in ethanol created in the morning, single samples
of 2mL each were pipetted into 2mL plastic vials (Quality Scientific plastics product
code: 522), which were used to transport samples to exposure sites. For control purposes
one extra sample was put into a vial and treated similarly to the rest (except that it was
not exposed), so as to receive the same incidental exposure that the other samples were
exposed to. Every attempt was made however, to avoid any incidental exposure of the
samples during transport to and from the study sites. For transport the plastic vials were
each placed inside black paper sleeves. The samples were then placed into the upper tray
of a carrying case, which was also fashioned with a black paper cover. And finally the
lid of the case remained closed during transport.
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Figure 35: Plastic vial halfway inside of black sleeve (left) and fully inserted vials inside carrying case (right)
Once at the study site, samples were transferred from their plastic vials with black sleeves
into the 4mL quartz cuvettes.
Four samples were exposed at each location. This number was limited by the
availability and cost of various supplies: the cuvettes themselves, 7-DHC, and chemicals
used during HPLC sample analysis. Cuvettes containing sample solution were placed on
top of the same level surface as the erythemal UV detector one by one and the exposure
timer was started as soon as the fourth cuvette was positioned for exposure. The cuvettes
were positioned horizontally as shown in the following image.
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Figure 36: Example of equipment set-up during data collection
The group of samples was left alone for an exposure of twenty minutes while
measurements of erythemal UV and the solar UV spectrum were collected. At the end of
these twenty minutes the samples in the cuvettes were taken one by one and transferred
into new plastic vials, and then placed back into the black sleeves and carrying case. The
samples were transferred into the new vials in the same order as they were placed out for
exposure (i.e. the first sample placed out for exposure was the first sample removed).
This means that there was at most a few seconds difference in the exposure times
between any two samples. After the exposed samples were secured in their new plastic
vials the cuvettes were cleaned using HPLC grade ethanol and the process was repeated
for the following exposure.
After each set of exposures (morning, noon, afternoon) samples were returned to
the laboratory in order to let thermo-isomerisation occur before analysis. When human
skin is exposed to sunlight, the thermal reaction that 7-DHC undergoes is thought to last
up to 24 hours. Therefore, in order to replicate as accurately as possible the process that
occurs in the human body, each sample was kept at 37 degrees Celsius (human body
temperature) for 24 hours before analysis. The control sample was also placed in the
incubator for 24 hours in the same manner as the exposed samples. The transfer of
samples between the carrying case and the sample incubator was completed under UV-
free lighting.
95
Prior to analysis, all samples were removed from the incubator, transferred into
labelled analysis vials, and loaded into the HPLC system’s auto-sampler. This procedure
was again completed under UV-free lights. Vitamin D dosimeter samples were then
analysed through the use of the HPLC system.
Monitoring of air pollution and environmental conditions
Measurements of air pollution and environmental conditions were continuously
collected at the respective stations described in section 6.1 throughout the duration of this
study, and data that corresponded to the date and time of in-vitro model exposures and
UV measurements was obtained from these monitoring stations. Air pollution data
obtained was of two forms, visibility reducing particles and PM-10 particles.
Measurements of temperature and humidity were collected from the weather station.
8.5. Data entry and cleaning
During data collection, time of reading and values of erythemal UV, along with
notes regarding cloud cover and traffic patterns were recorded on data collection sheets.
Along with this, UV spectrum data was recorded and saved to an Excel spreadsheet.
From these spreadsheets, which contained values representing EM radiation at each
wavelength between 280nm and 900nm, values were summed in order to obtain a single
value representing total UVB radiation and total UVA radiation. In regards to samples
from the in-vitro model of vitamin D synthesis: upon completion of laboratory analysis,
values of 7-DHC and cholecalciferol were recorded on data collection sheets. At the end
of the observational phase of the study other data was collected from outside sources and
added to data collection sheets, this information included: visibility reducing particles,
PM-10 particles, temperature, humidity, and solar zenith angle at time of data collection.
From these data collection sheets information was entered into an SPSS
workbook. All data was entered first by Alex McKinley and then independently re-
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entered by ASHRL assistant Claire Falampin. These entries were compared, and upon
finding a discrepancy between the two versions the appropriate data collection sheet was
referred to in order to correct any incorrectly entered data points. This SPSS workbook
was then used to analyse the collected data.
8.6. Data analysis
Data analysis consisted of uni-variate and bi-variate statistical comparisons as
well as linear regression modelling. To begin, each variable was analysed separately.
For each respective variable independent T-tests were used to compare the average value
from the group of urban canyon sites (1-4) to the average value from the suburban site.
Data was then broken down further with respect to time of collection and specific site and
these respective averages were computed. Following from this, correlations between
different variables were investigated. The correlation statistic used during this procedure
was the Pearson’s correlation coefficient (r). In addition, scatter plots showing linear
trend lines and coefficients of determination (r2) were implemented during analysis.
Finally, linear regression modelling was used in order to determine which of the
measured variables predicted the production of cholecalciferol and the depletion of 7-
DHC during this study.
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9. Quantification of UV exposure and vitamin D synthesis in an urban canyon
A total of 121 distinct study site visits occurred between June 22, 2007 and
August 30, 2007. As described in section 8.4 data was collected using the vitamin D
dosimeter (measuring both the amount of cholecalciferol produced during exposure and
the amount of 7-DHC depleted during exposure), the handheld erythemal detector
(measuring erythemal UV), the portable CCD spectrometer (measuring UVA, UVB, and
total UV radiation), and acquired from the pollution monitoring station (measuring PM-
10 particles and visibility reducing particles), and the weather station (measuring
temperature and relative humidity). During each of these study site visits four vitamin D
dosimeter samples were exposed simultaneously, resulting in the exposure of 484 vitamin
D dosimeter samples. After each site visit the four vitamin D dosimeter samples were
analysed to determine cholecalciferol production and 7-DHC depletion. This resulted in
four measures of cholecalciferol production and four measures of 7-DHC depletion from
each site visit. These sets of four measurements were then averaged with the result being
121 values representing the average amount of cholecalciferol produced and the average
amount of 7-DHC depleted at each site visit.
For analysis the data was organized by study site and time of data collection in
order to compare results. When organized by study site, data was analysed for individual
sites and with data from the four primary urban canyon sites combined into a single
group. These four sites were combined together for analysis in order to give an overall
representation of the urban canyon environment. When organized by collection time,
data was analysed first with all times lumped together and then with data separated into
groups of samples exposed during the morning, at noon, and in the afternoon. These
categorizations are used during the discussion of results in the following sections. Table
6 shows the breakdown of the 121 site visits by site and time of day. The sites are
labelled in the same manner as in section 8.3 so as to facilitate recognition.
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Number of measurements organized by time of data collection
Site Sample size
morning
Sample
size noon
Sample size
afternoon
Overall
sample size
1 (primary urban
canyon site)
8 7 7 22
2 (primary urban
canyon site)
7 7 8 22
3 (primary urban
canyon site)
6 7 5 18
4 (primary urban
canyon site)
7 7 8 22
5 (public open
space in urban
canyon)
3 3 2 8
Suburban (athletic
field)
9 10 10 29
Sum of sites 1-4 28 28 28 84
Total for part of
day
40 41 40 121
Table 6: Measurement situations broken down by time of day and site
As seen in table 6, the sample size for data collected at site 5 (the public open space in the
urban canyon) is smaller than that collected for the other sites. Data was collected at this
site less frequently than at the others due to time constraints. For this reason, during the
discussion of results in the following sections data collected at site 5 is mentioned
99
separately from that collected at the primary urban canyon collection locations - sites 1-4.
In addition this site was selected specifically as a location in the urban canyon that
receives greater amounts of direct sunlight than the average location.
The analysis of this data was conducted by first examining total UV, erythemal
UV, and vitamin D production independently and then moving on to the interactions
between these measures. Finally, linear regression models analysing the factors that
influenced cholecalciferol production and 7-DHC depletion were developed.
9.1. Measurements of spectral UV radiation
The ambient UV radiation was measured in one nanometre (nm) steps across the
entire UV spectrum and this data was then summed into wave bands of total UV (100 –
400nm), UVA (320 – 400nm), and UVB (280 – 320nm). Data for each of these wave
bands was then categorized for analysis as: total data from sites 1-4 vs. total suburban
data, time specific data (morning, noon, and afternoon), site specific data, and finally site
and time of day specific.
Total CBD data vs. total suburban data
Through the entire course of data collection the average total un-weighted UV
measured at sites 1-4 during a single measurement was 0.25W/m2, while the suburban
site recorded an average of 1.03W/m2. Of this the UVA waveband made up the majority
of that received in both the CBD and at the suburban location. The average UVA
received during a single measurement in the urban canyon was 0.24W/m2 and the average
UVB was 0.01W/m2, while the average UVA measured at the suburban site was
1.00W/m2 and the average UVB was 0.03W/m2.
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Average UV received during a single measurement over all data collection times
Site Total UV (W/m2)
UVA (W/m2) UVB (W/m2) UVB / UVA
Sites 1-4 (stdev) 0.25 (0.21)* 0.24 (0.21)* 0.01 (0.007)* 0.048 (0.026)*
Suburban (stdev) 1.03 (0.52)* 1.00 (0.50)* 0.03 (0.016)* 0.026 (0.007)*
Sites 1-4 as a
percentage of
suburban
24.3% 24.0% 33.3%
*P-value < 0.01
Table 7: Summary of total UV, UVA, and UVB measurements for all data collection times showing lower urban canyon values
It is interesting to note that, while only contributing a small portion of the total UV
measured at all sites, the UVB at sites 1-4 made up a greater percentage of the total UV
than that measured at the suburban site.
CBD data vs. suburban data as a function of time of day
When categorized based on the time of exposure (morning, noon, and afternoon)
noon exposures received the greatest amount of UV and afternoon exposures received the
least. This trend is seen for all three measures of UV discussed and it shows that the
difference between the average noon exposure and the average morning exposure is much
less than the difference between the average noon exposure and the average afternoon
exposure.
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Summary of average UV received during morning, noon, or afternoon exposure
Site Total UV (W/m2)
UVA
(W/m2)
UVB
(W/m2) UVB / UVA
Morning
Sites 1-4 0.27 0.26 0.01 0.038
Suburban 1.18 1.15 0.03 0.026
Sites 1-4 as a
percentage of
suburban
23.9% 22.6% 33.3%
Noon
Sites 1-4 0.32 0.31 0.01 0.031
Suburban 1.47 1.43 0.04 0.027
Sites 1-4 as a
percentage of
suburban
21.7% 21.7% 25.0%
Afternoon
Sites 1-4 0.17 0.16 0.01 0.063
Suburban 0.45 0.44 0.01 0.023
Sites 1-4 as a
percentage of
suburban
37.8% 36.4% 100%
Table 8: Average UV measurements from urban canyon sites and suburban site categorized by time of exposure (morning, noon, and afternoon) showing lower urban canyon values
Within this data there are two key results. The first is the fact that measurements taken in
the afternoon are much lower than those taken in the morning. The second is the
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difference between the percentage of suburban radiation received in the urban canyon
during morning or noon exposures and afternoon exposures.
One might expect the values measured at 9am and 3pm to differ with similar
magnitude from those recorded at noon, as solar zenith angles (described in section 2.1)
were at their smallest during data collection close to 12:00pm. However, during this
study the average solar zenith angle associated with data collection in the morning was
56° and the average solar zenith angle associated with data collection during the
afternoon was 70°. This difference is due to the fact that data collection times were
shifted toward a later time on both ends of the day (average time of morning data
collection: 09:40, and afternoon data collection: 15:28). This shift places the morning
collection closer to the peak solar zenith angle and the afternoon collection further from it
and explains the difference between morning and afternoon measurements.
When comparing morning and noon exposures the percentage of suburban
radiation received in the urban canyon is very similar for all three measures of UV
radiation; however during afternoon exposures these percentages increase. During the
morning and noon exposures the urban canyon received an average of approximately
22% of the total UV and UVA that the suburban site received and 25-33% of the UVB,
however during afternoon exposures the urban canyon received an average of
approximately 37% of the total UV and UVA and 100% of the UVB. A possible
explanation for this finding is that as the percentage of ambient diffuse UV increases the
effect the urban canyon has on UV decreases, however the fact that the average morning
and noon values are so similar suggests that this may not be the entire cause.
Site specific data
When comparing individual sites across all times the suburban site still shows the
highest average levels of total UV, UVA, and UVB. The public open space shows the
second highest levels of radiation, receiving an average of more than double the amount
of total UV radiation measured at three of the four principle sites.
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Summary of average UV received during a single measurement: data categorized by study site
Site 1 (Watts/m2)
Site 2 (Watts/m2)
Site 3 (Watts/m2)
Site 4 (Watts/m2)
Public open space
(Watts/m2)
Suburban (Watts/m2)
Sites 1-4 (Watts/m2)
UVA 0.23 0.29 0.18 0.28 0.57 1.00 0.24
UVB 0.009 0.012 0.010 0.012 0.018 0.028 0.010 Total UV 0.24 0.30 0.19 0.29 0.59 1.03 0.25
UVB / UVA 4.3% 3.4% 5.6% 3.6% 3.5% 3.0% 4.2%
Table 9: Average UV measurements categorized by individual study site (UVB data taken to 3 significant figures to show variation between site averages).
Site 3 received the least amount of average UVA radiation while site 1 received the least
amount of average UVB radiation. When this information is further broken down by
time of day it can be seen that for each time period (morning, noon, afternoon) the site
receiving the lowest amount of UVA did coincide with the site receiving the lowest
amount of UVB.
From analysis of the data by site and time of exposure it is found that no site
consistently received more or less UV than the other sites. When compared with the
suburban site however, sites 1-4 received a significantly lower average amount of UVA,
UVB, and total UV. The morning and noon data collections showed a much greater
difference between urban canyon measurements and suburban measurements than the
afternoon measurements. The relative UV exposure measured at the sites can be viewed
in the following charts. The first three charts display total UV, UVA, and UVB exposure
contrasting suburban and urban canyon sites. The final three charts show total UV,
UVA, and UVB data, but only for sites 1-4 (the urban canyon sites) displaying smaller
scale variations between these sites.
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Figure 37: Average total UV radiation at all sites compared across time of day
105
Figure 38: Average UVA radiation at all sites compared across time of day
106
Figure 39: Average UVB radiation at all sites compared across time of day
107
Figure 40: Average total UV radiation at sites 1-4 compared across time of day
108
Figure 41: Average UVA radiation at sites 1-4 compared across time of day
109
Figure 42: Average UVB radiation at sites 1-4 compared across time of day
110
From these charts two important results can be derived: a) the relatively tight cluster of
values from the urban canyon sites compared with the suburban values, and b) the
relatively low values measured at all sites during the afternoon data collection.
Variations exist between the four urban canyon sites, however these are relatively small
when compared with the difference between the urban canyon sites and the suburban site.
During morning and noon observations the suburban site received more than twice the
highest average value at any of the sites 1-4 for measurements of total UV, UVA, and
UVB. In the afternoon though, all sites measured low levels of UV radiation, and while
the suburban site received more, the difference between it and sites 1-4 was far less. The
public open space received more UV than sites 1-4 during the noon and afternoon data
collections, but not during the morning when the available direct sunlight passed between
two buildings and did not come from directly overhead. During noon data collection the
average UV measured in the open square did not reach the level measured at the
suburban site, but was significantly greater than that measured at sites 1-4.
When average UVB was taken as a percentage of average UVA the suburban
location measured the lowest percentage of UVB for all times of the day. At the
suburban site, average UVB measured was approximately 2-3% of the average UVA
measured, while in general the urban canyon sites saw 1.5-2 times that percentage of
UVB. The only urban canyon sites that had values similar to those of the suburban site
were the public open space during the noon and afternoon measurements and site 1
during the afternoon collection, each of which were subject to direct sunlight at these
times.
111
Figure 43: Average UVB as a percentage of total UV at all sites compared across time of day
112
These results suggest that direct UV radiation contains a lower percentage of
UVB than diffuse UV. However as seen in the previous pages, this higher percentage of
UVB in diffuse situations did not translate to greater absolute amounts of UVB within the
urban canyon compared to the suburban site.
9.2. Measurements of erythemal UV radiation
Erythemal UV is that which is described by the erythemal action spectrum and can be
considered damaging UV radiation (described in section 2.2). Data was integrated over
the entire exposure period (20 minutes) and a single value of erythemal UV was recorded
for each exposure. This data was then categorized for analysis in a similar fashion to the
UV spectral data described in section 9.1: total data from sites 1-4 vs. total suburban data,
time specific data (morning, noon, and afternoon), site specific data, and finally site and
time of day specific. Analysis of erythemal UV data showed similar results to that of the
UV spectral data: at the urban canyon locations significantly less erythemal UV was
measured than at the suburban site.
Total data from sites 1-4 vs. total suburban data
Over all data collection at sites 1-4 the average erythemal UV recorded during a
single measurement was 0.095 MED (MED described in section 3.1), while the average
erythemal UV recorded during a single measurement at the suburban site was 0.375
MED. This difference is significant with a p-value of less than 0.01. Viewed as a
percentage the average erythemal value for a single measurement at sites 1-4 was
approximately 25% of the average value measured at the suburban site.
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Data categorized by time of data collection
When the erythemal data is categorized in terms of time of data collection
(morning, noon, afternoon) the highest levels of average UV are found at noon, the
second highest in the morning, and the lowest levels of average UV in the afternoon.
These trends were found for both the average of sites 1-4 and the suburban site. As with
the UV spectral data the difference between the urban canyon sites and the suburban site
is very pronounced during both the morning and noon measurements, but less so in the
afternoon.
Average erythemal UV received during single measurement: Sites 1-4 compared
with Suburban site
Site Morning (MED) Noon (MED) Afternoon (MED)
Sites 1-4 average 0.093 0.152 0.040
Suburban 0.444 0.661 0.109
Sites 1-4 as a percentage
of suburban
21% 23% 37%
Table 10: Erythemal UV categorized by time of exposure showing lower erythemal UV in the urban canyon
The average percentage of suburban erythemal UV found in the urban canyon was
highest (37%) in the afternoon, and was much lower in the morning (21%) and at noon
(23%). From table 10 it is also evident that there is a much wider range of average
erythemal UV values encountered at the suburban site than in the urban canyon.
114
Erythemal UV categorized by individual site and time of day
If erythemal UV measurements are investigated further, variations between sites
similar to those found with the spectral measurements present themselves. Average
suburban measurements were significantly greater than those seen at the various urban
canyon locations; however the difference between urban and suburban locations was less
in the afternoon than in the morning or at noon. No urban site received the highest or
lowest average level of erythemal UV through the entire day, and in fact the site
measuring the lowest average value in the morning (site 1: 0.061 MED) and at noon (site
1 and site 3: 0.119 MED), received the highest amount in the afternoon (site 1: 0.066
MED). Site 1 was also the only site to measure an average level of erythemal UV in the
afternoon greater than that measured in the morning or at noon. The following charts
show these relationships.
115
Figure 44: Average erythemal UV at each site categorized by time of exposure
116
Figure 45: Average erythemal UV at sites 1-4 categorized by time of exposure
117
As with the UV spectral measurements, the erythemal UV data for sites 1-4 is clustered
relatively close together when compared with that from the suburban location. During
noon measurements the public open space received a significantly greater amount of
average erythemal UV than urban canyon sites 1-4, but this trend did not hold for the
morning or afternoon measurements.
From these results it can be seen that erythemal UV measured in the urban canyon
was significantly less than that measured at the suburban location. This result agrees
with the results seen from the total UV, UVA, and UVB measurements in section 9.1.
9.3. Measurements involving the vitamin D dosimeter
The samples from the vitamin D dosimeter were analysed using the HPLC system
and the amount of cholecalciferol (vitamin D) produced and amount of 7-DHC depleted
were recorded. These data sets were then analysed in similar fashion to the previous UV
radiation data: the information was categorized in terms of total data from sites 1-4 vs.
total suburban data, time specific data (morning, noon, and afternoon), and site and time
of day specific data. Along with this analysis, data from sites in the urban canyon was
paired with the nearest data collection at the suburban site and the difference between
recorded measures was studied.
Total data: sites 1-4 vs. suburban data
Over the entire course of data collection it was found that there were significant
differences between the average amount of cholecalciferol produced at sites 1-4 and at
the suburban site and between the amount of 7-DHC depleted at sites 1-4 and at the
suburban site. These results coincide with the previously discussed differences in UV
spectral measurements and erythemal UV measurements. At sites 1-4 the average
amount of cholecalciferol produced during a single exposure was 0.128μg/mL, while the
118
average cholecalciferol produced during an exposure at the suburban site was
0.536μg/mL (p-value 0.001). At sites 1-4 the average amount of 7-DHC depleted during
an exposure was 24.7μg/mL and the average amount depleted at the suburban site was
77.7μg/mL (p-value 0.001). Viewed as percentages the average amount of
cholecalciferol produced at sites 1-4 was 24% of that produced at the suburban site and
the average amount of 7-DHC depleted at sites 1-4 was 32% of that depleted at the
suburban site. These results also show that only a very small amount of depleted 7-DHC
is actually transformed into cholecalciferol. The majority is changed into lumisterol,
tachysterol, or one of the many other biologically inactive photo-products of UV’s
interaction with 7-DHC.
Data categorized by time of exposure
When this data is broken down in terms of the time of the exposure trends similar
to those seen in the UV radiation data present themselves. In absolute terms there is a
large difference between the average of the data collected at sites 1-4 and the average of
that collected at the suburban site for morning and noon collections, but a lesser
difference between data collected at these different sites during the afternoon. In relative
terms the morning and noon exposures produced approximately 20% as much
cholecalciferol at sites 1-4 as at the suburban site. However in the afternoon this value
jumped to approximately 45%. Throughout the day approximately 30% as much 7-DHC
was depleted at sites 1-4 as at the suburban site. Tables 11 and 12 show these
relationships.
119
Average cholecalciferol production during a single measurement categorized by
time of exposure
Morning
(μg/mL)
Noon
(μg/mL)
Afternoon
(μg/mL)
Sites 1-4 0.114 0.219 0.051
Suburban 0.587 0.913 0.108
Sites 1-4 as a percentage of suburban 20% 24% 47%
Table 11: Average cholecalciferol production at sites 1-4 compared to that at the suburban site
Average 7-DHC depletion during a single measurement categorized by time of
exposure
Morning
(μg/mL)
Noon
(μg/mL)
Afternoon
(μg/mL)
Sites 1-4 26.6 31.4 16.0
Suburban 85.6 97.2 50.3
Sites 1-4 as a percentage of suburban 31% 32% 32%
Table 12: Average 7-DHC depletion at sites 1-4 compared to that at the suburban site
The most important result of this analysis is the percentage difference in cholecalciferol
production found between the morning/noon exposures and the afternoon exposures.
This difference means that during situations with the lowest UV levels (afternoon) the
cholecalciferol production at sites 1-4 was much closer to that at the suburban site (still a
little less than 50% however) than during situations of higher UV levels. This result
corresponds to what was found in the previous analysis of the UV radiation data: the
120
difference between the suburban site and sites 1-4 was much smaller in the afternoon than
during the morning or at noon.
An additional result is that the percentage of 7-DHC depleted at the urban canyon
sites in relation to the suburban site remained constant throughout the day even though
the percentage of cholecalciferol produced varied. This shows that cholecalciferol was
not the only photoproduct produced during the depletion of 7-DHC (section 2.4 discusses
the processes that result in the production of cholecalciferol, and section 6.1 shows the
output from a sample run with the other photoproducts labelled).
Cholecalciferol and 7-DHC data categorized by site and time of day
When data is broken down and individual sites are viewed the results are similar
to those seen in the erythemal and spectral UV sections. In the case of either outcome of
UV exposure there is no site that showed the greatest or least average cholecalciferol
production or 7-DHC depletion at all measurements during the day. The same relative
clustering of data from sites 1-4 in comparison to the suburban site occurs with this
cholecalciferol and 7-DHC data. For all three parts of the day the site that produced the
greatest average amount of cholecalciferol is also the site that saw the greatest average
depletion of 7-DHC. These relationships can be seen in table 13 and figures 46-49.
121
Average cholecalciferol production and 7-DHC depletion during a single
measurement categorized by specific site and time of exposure
Morning
Site 1 Site 2 Site 3 Site 4
Public
open
space
Suburban Sites 1-4
average
Cholecalciferol 0.066 0.163 0.119 0.108 0.086 0.587 0.114
7-DHC 17.7 39.8 25.3 25.0 27.8 85.6 26.6
Site 1 Site 2 Site 3 Site 4
Public
open
space
Suburban Sites 1-4
average
Cholecalciferol 0.170 0.327 0.132 0.227 0.383 0.913 0.219
7-DHC 23.6 43.3 25.4 33.0 68.0 97.2 31.4
Afternoon
Site 1 Site 2 Site 3 Site 4
Public
open
space
Suburban Sites 1-4
average
Cholecalciferol 0.083 0.065 0.023 0.029 0.084 0.108 0.051
7-DHC 23.9 17.3 10.3 12.4 38.7 50.3 16.0
Table 13: Average cholecalciferol production and 7-DHC depletion. All data is displayed in units of μg/mL.
122
Figure 46: Cholecalciferol production vs. time of day for each site
123
Figure 47: 7-DHC depletion vs. time of day for each site
124
Figure 48: Cholecalciferol production vs. time of day for sites 1-4
125
Figure 49: 7-DHC depletion vs. time of day for sites 1-4
126
Of sites 1-4, site 2 saw more cholecalciferol production and 7-DHC depletion than the
others during both morning and noon data collections, however site 1 showed the most of
each during the afternoon. The difference between average cholecalciferol production
and average 7-DHC depletion at site 2 and at sites 1, 3, and 4 is relatively large during the
morning and noon collections, however when compared to the suburban site it is still less
than half in each instance.
Comparison between data collected at sites 1-4 and paired exposures at the
suburban site
Data collected during each specific urban canyon measurement was paired to a
specific measurement collected at the suburban site. For each data point collected in the
urban canyon the suburban measurement occurring at the same time of day (morning,
noon, afternoon) on the nearest date was selected and the two points were paired together
for comparison. This pairing of points was done irrespective of weather conditions (i.e.
sites were not paired based on cloud cover or other factors, date was the only factor
used). The difference between the measurement taken at the suburban site and the
measurement taken at the urban site was then calculated. Therefore any positive value
shows that the suburban site either saw greater cholecalciferol production or greater 7-
DHC depletion than its paired urban canyon site. This process was undertaken in order to
compare measurements collected in close temporal proximity, as previous discussion
dealt only with data collected over the entire course of measurement.
The results of this analysis of paired sites were similar to other results in this
section. On average more cholecalciferol was produced at the suburban location than at
the urban canyon sites and on average more 7-DHC was depleted at the suburban site
than at the urban canyon sites. The largest average differences between the paired sites
occurred during the noon measurements. The afternoon measurements showed average
differences that were much smaller than those seen in the morning or at noon.
127
Average of the difference between paired suburban and urban canyon sites: cholecalciferol production and 7-DHC depletion
All data displayed in units of μg/mL
Morning
Site 1 Site 2 Site 3 Site 4 Public open space
Sites 1-4 average
Cholecalciferol
difference 0.452 0.344 0.387 0.396 0.410 0.397
7-DHC
difference 70.8 46.3 62.5 61.1 63.4 60.5
Noon
Site 1 Site 2 Site 3 Site 4 Public open space
Sites 1-4 average
Cholecalciferol
difference 0.726 0.630 0.745 0.734 0.552 0.708
7-DHC
difference 71.5 55.3 69.9 65.7 34.5 65.6
Afternoon
Site 1 Site 2 Site 3 Site 4 Public open space
Sites 1-4 average
Cholecalciferol
difference 0.030 0.026 0.059 0.061 -0.007 0.042
7-DHC
difference 20.7 25.8 36.3 30.7 11.1 28.3
Table 14: Average difference between suburban and urban site paired sites
128
As can be seen in the afternoon data, the public open space actually averaged more
cholecalciferol production than the suburban site. Absolute production of cholecalciferol
was low at all sites during the afternoon and the number of data points collected at the
public open space was very small as well. The other data points present a clear trend,
however. Data from all other sites and times of day show suburban cholecalciferol
production and 7-DHC depletion to be greater than that in the urban canyon.
9.4. Measurements of air pollution and environmental
conditions
The air pollution monitoring station and the weather station collected data
constantly throughout the day. The data corresponding to the times measurements were
taken at the different CBD sites and at the suburban site were selected and matched with
vitamin D dosimeter and UV data. Air pollution, temperature, and humidity data points
represented the overall air pollution and environmental conditions in the central Brisbane
area during each measurement situation and were not specific to each individual
measurement site. These data were then treated in the same fashion as vitamin D
dosimeter and UV data during analysis, that is to say, data was categorized by site and
time of exposure. The results of the analysis of air pollution data do not coincide with the
results seen in the previous sections and the theory that higher levels of air pollution in
the urban canyon would reduce the amount of UV radiation measured there when
compared to the suburban site. Instead, average measurements of air pollution that
coincided with urban canyon measurement situations were lower than those that
coincided with suburban measurement situations, which could be a random finding or
reflect typically higher air pollution on Tuesdays and Thursdays compared to other
weekdays.
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Pollution measurements: PM-10 and visibility reducing particles
Average values of both PM-10 sized particles and visibility reducing particles
associated with urban canyon measurement sites were lower than those associated with
measurement at the suburban site. The difference between average PM-10 values was
significant while the difference between visibility reducing particles was not.
PM-10 and visibility reducing particles
PM-10 (μg/m3) Visibility reducing particles (visibility loss/Mm)
Average sites 1-4 (stdev) 15.5 (6.6)* 17.6 (17.3)
Average suburban site (stdev) 21.0 (8.0)* 27.6 (35.4)
* P-value = 0.01
Table 15: Comparison of average air pollution data between sites 1-4 and suburban site
When air pollution data was broken down by time of day and by site the trend of greater
amounts of pollution being associated with measurements at the suburban site held for
both PM-10 and visibility reducing particles.
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Summary of average air pollution measurements categorized by time of exposure
Site PM-10 (μg/m3) Visibility reducing particles (visibility loss/Mm)
Morning
Sites 1-4 15.7 25.3
Suburban 20.2 51.9
Noon
Sites 1-4 15.9 13.0
Suburban 21.2 16.7
Afternoon
Sites 1-4 15.5 13.7
Suburban 21.3 16.9
Table 16: Average air pollution measurements categorized by time of exposure
Urban canyon data was collected on Mondays, Wednesdays, and Fridays and suburban
data was collected on Tuesdays and Thursdays during this study. It is possible that a
trend of overall air pollution in Brisbane associated with these days influenced this data.
In addition, the National Environmental Protection Council has set an air quality standard
for PM-10 particles, which is 50μg/m3, a value more than twice that of the average PM-
10 concentrations measured in conjunction with either the urban canyon or suburban
measurement situations. The highest PM-10 value measured at any time during this
study was 35.8μg/m3. Therefore the measurements during this study were not taken
during situations of high air pollution involving PM-10 particles. Visibility reducing
particles do not have a standard to measure against.
Environmental measurements: Temperature and humidity
Temperature and humidity measurements acquired from the weather station were
associated by date and time with measurements taken at the various study sites in the
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same manner as air pollution data. Measurements taken at the suburban site were
associated with average temperatures approximately one degree higher than that
associated with measurements from the urban canyon. There was a difference of
approximately 1% found between measurements of relative humidity in the urban canyon
and at the suburban site. Neither of these differences between means were found to be
significant.
Temperature and humidity measurements
Temperature (C) Relative humidity (%)
Average sites 1-4 (stdev) 18.7 (3.4) 43.9 (15.8)
Average suburban site (stdev) 19.9 (3.0) 44.5 (14.4)
Table 17: Average temperature and humidity measurements compared between urban canyon and suburban site
Further break down of temperature and humidity measurements revealed no great
difference between measurements associated with urban canyon and suburban sites.
9.5. Correlations between measurements
In sections 9.1 – 9.3 data has been analysed in terms of single variables only, but now
bi-variate associations between variables are discussed. This section investigates the
correlations present between cholecalciferol production, 7-DHC depletion, erythemal
UV, spectral UV, and the measurements of air pollution and environmental conditions.
Results are displayed for data collected at all sites and then this is broken down to show
the differences between data collected at the primary urban canyon locations (sites 1-4)
and at the suburban site.
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Cholecalciferol production as it relates to UV, air quality, and environmental
measures
For data collected at all sites, cholecalciferol measurements were shown to
correlate strongly with UVA, UVB, total UV, and erythemal UV measurements, with the
strongest correlation being between cholecalciferol and erythemal UV data.
Measurements of cholecalciferol did not correlate strongly with air pollution or
environmental data.
Pearson’s correlations between cholecalciferol and other variables at all sites
Total UV UVA UVB Erythemal UV
Cholecalciferol .885** .883** .911** .974**
PM10
Visibility
reducing particles
Temperature Humidity
Cholecalciferol .176** .010 .311** -.082
** Correlation is significant at the 0.01 level (2-tailed)
Table 18: Pearson's correlations between cholecalciferol production and other variables
All correlations between cholecalciferol and UV measures were positive and significant
at the 0.01 level. The difference between the strength of correlations found between
cholecalciferol data and the measurements of total UV, erythemal UV, UVA, and UVB
(first row) and lack of correlations between cholecalciferol data and the pollution and
environmental data (second row) is very striking. The strong correlations between
cholecalciferol production and UV measurements are examined further through the
following three scatter plots.
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Figure 50: Cholecalciferol produced plotted against UVA radiation for all sites
134
Figure 51: Cholecalciferol produced plotted against UVB radiation for all sites
135
Figure 52: Cholecalciferol produced plotted against erythemal UV radiation for all sites
136
Each of these charts shows a large cluster of data in the range of low cholecalciferol
production and low UV exposure, which is representative of the large amount of data
collection that took place in the urban canyon. The data points representing relatively
greater amounts of UV radiation are mostly those from the suburban site.
When data is separated between that collected within the urban canyon (sites 1-4)
and that collected at the suburban site, results show that stronger correlations are
associated with data collected at the suburban site than with data collected at sites 1-4.
Table 19 shows correlations between cholecalciferol and other variables separated into
urban and suburban measurements.
Pearson’s correlations between cholecalciferol production and other variables at sites1-4 and suburban site
Total UV UVA UVB Erythemal UV
Cholecalciferol sites 1-4 .694** .689** .741** .929**
Cholecalciferol suburban .909** .906** .957** .974**
PM10 Visibility reducing particles
Temperature Humidity
Cholecalciferol sites 1-4 .186* .035 .289** -.092**
Cholecalciferol suburban -.145 -.156 .309* -.130*
** Correlation is significant at the 0.01 level (2-tailed)
* Correlation is significant at the 0.05 level (2-tailed)
Table 19: Pearson's correlations between cholecalciferol production and other variables compared between urban canyon measurements and suburban measurements
Table 19 reinforces the readings from Table 18 and shows that the pollution and
environmental measurements do not correlate strongly with cholecalciferol production in
either the urban canyon or at the suburban site. Correlations between cholecalciferol
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production and UV measures were greater at the suburban site than in the urban canyon,
but both sites were still strong. Erythemal UV showed again to have the strongest
correlation with cholecalciferol production.
7-DHC depletion as it relates to UV, air quality, and environmental measures
As with cholecalciferol production measurements, measurements of 7-DHC
depletion also correlated strongly with measurements of total UV, UVA, UVB, and
erythemal UV. The most notable result of analysis of 7-DHC depletion data collected at
all sites is that 7-DHC depletion correlated more strongly with measurements of UVA
radiation than did cholecalciferol production. Along these same lines, 7-DHC depletion
does not correlate with UVB measurements as strongly as cholecalciferol production
does. This is in accordance with expectations because energy in the UVB band initiates
the production of cholecalciferol, whereas both UVA and UVB can break apart the 7-
DHC molecule.
Pearson’s correlations between 7-DHC depletion and other variables at all sites
Total UV UVA UVB Erythemal UV
7-DHC .922** .922** .845** .895**
PM10 Visibility reducing particles
Temperature Humidity
7-DHC .261 .178 .198 -.082
** Correlation is significant at the 0.01 level (2-tailed)
Table 20: Pearson's correlations between 7-DHC depletion and other variables
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As with the cholecalciferol depletion data, all measurements of UV radiation (first row)
correlated highly with 7-DHC depletion. In addition, none of the correlations between 7-
DHC and the air pollution or environmental variables were strong or significant at the
0.01 level. The following scatter plots further describe the strong correlations seen
between 7-DHC depletion and the UV measurements.
139
Figure 53: 7-DHC depleted plotted against UVA radiation for all sites
140
Figure 54: 7-DHC depleted plotted against UVB radiation for all sites
141
Figure 55: 7-DHC depleted plotted against erythemal UV radiation for all sites
142
As with the scatter plots dealing with cholecalciferol, there is a large cluster of data on
each of these in the section associated with low values of 7-DHC depletion and low
levels of UV radiation. However, what is different between these plots and the
cholecalciferol plots is that UVA shows the strongest correlation with 7-DHC depletion.
Of the UV measures UVA showed the weakest correlation with cholecalciferol.
When data is separated into that collected in the urban canyon (sites 1-4) and that
collected at the suburban site the results differ from those seen with the cholecalciferol
measurements. In this case the measurements taken in the urban canyon correlate more
strongly than those from the suburban sites. This data is shown in table 21 below.
Pearson’s correlations between 7-DHC depletion and other variables at all sites
Total UV UVA UVB Erythemal UV
7-DHC sites 1-4 .738** .737** .667** .829**
7-DHC suburban
.925** .925** .874** .880**
PM10 Visibility reducing particles
Temperature Humidity
7-DHC sites 1-4 .115* .110* .099 .018
7-DHC suburban
-.135 .105 -.004 -.109
** Correlation is significant at the 0.01 level (2-tailed)
* Correlation is significant at the 0.05 level (2-tailed)
Table 21: Pearson's correlations between 7-DHC production and other variables compared between urban canyon measurements and suburban measurements
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This analysis shows that correlations between pollution and environmental measurements
(second row) and 7-DHC depletion remained weak when the data was broken down by
site. At the suburban site erythemal UV correlated most strongly with 7-DHC depletion
however in the urban canyon UVA radiation correlated most strongly.
Correlation between cholecalciferol production and 7-DHC depletion
In addition to strong correlations between each of these variables and the different
UV measurements there also exists a strong correlation between cholecalciferol
production and 7-DHC depletion.
Correlation between cholecalciferol production and 7-DHC depletion
All sites Urban canyon (sites 1-4) Suburban
Pearson’s
correlation .858** .840** .835**
** Correlation is significant at the 0.01 level (2-tailed)
Table 22: Pearson's correlation between cholecalciferol production and 7-DHC depletion
The correlation between cholecalciferol production and 7-DHC depletion does not vary a
great deal between the urban canyon sites and the suburban location. The following
scatter plot shows the strong linear relationship that exists between cholecalciferol
production and 7-DHC depletion at all sites.
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Figure 56: Cholecalciferol production plotted against 7-DHC depletion for all sites
145
As with previous charts, the cluster of data near the bottom left corner is mostly made
up of data collected within the urban canyon, and data points towards the upper right
(associated with larger amounts of cholecalciferol production and 7-DHC depletion)
were mostly collected at the suburban site.
9.6. Linear regression modelling
Finally, a series of linear regression models were produced relating the
measurements of UV radiation, air pollution, and temperature and humidity to the
production of cholecalciferol and the depletion of 7-DHC. These models were
produced using SPSS software. Separate models placed cholecalciferol production
and 7-DHC depletion as the single dependent variable and tested the influence of the
other measures as independent variables.
The variables entered into these models were chosen to be entered due to their
nature as objective measurements taken using calibrated scientific equipment.
Measures of building height, street length, percentage of sidewalk covered by
awnings, etc… were not included in these models because they were collected
subjectively by a single observer. These subjective measures were used only as a
description of the data collection environment (section 8.3). Even though they did not
correlate with other measures during this study the variables of air pollution,
temperature, and humidity were included in these models in order to allow the
modelling to show that they were also insignificant with respect to the outcomes
associated with the vitamin D dosimeter rather than basing this on assumption.
As erythemal UV incorporates both portions of the UVA and UVB spectra,
using all three of these variables at the same time could confound the results. Instead
multiple models were produced. The first input UVA and UVB together and the
second input erythemal UV on its own. Variables were entered into the models
together in a single entry procedure instead of a stepwise or hierarchal procedure.
This method was chosen so as to view the basic relationships between all independent
variables and the dependent variables.
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All sites
Using data collected at all sites throughout the entire course of data collection
the linear regression analysis showed that for both the production of cholecalciferol
and the depletion of 7-DHC that the only factors that had major impact were UVA,
UVB, or erythemal UV. The difference between the model that entered both UVA
and UVB and the model that entered only erythemal UV was not great, as each
predicted similar amounts of variance (approximately 85 – 95%) in cholecalciferol
production and 7-DHC depletion.
Linear regression model: Dependent variable cholecalciferol production at all sites
Independent variables entered: UVB, UVA, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .851
UVA UVB Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta .313* .605* .014 -.071* .066* .007
Independent variables entered: Erythemal UV, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .949
Erythemal UV Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta .964* .006 -.059* .041* .032*
*Significant at .05 level or lower
Table 23: Linear regression model: Dependent variable cholecalciferol production at all sites.
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Linear regression model: Dependent variable 7-DHC depletion at all sites
Independent variables entered: UVB, UVA, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .862
UVA UVB Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta .997* -.066 .062* -.011 -.090 .004*
Independent variables entered: Erythemal UV, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .847
Erythemal UV Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta .919* .051 .078* -.081* .028
*Significant at .05 level or lower
Table 24: Linear regression model: Dependent variable 7-DHC depletion at all sites
The models that combined UVA and UVB measurements saw UVB to be most
influential in the prediction of the production of cholecalciferol, while UVA had the
only major significant influence in terms of 7-DHC depletion. The model
incorporating erythemal UV did predict cholecalciferol production better than the
combined UVA and UVB model, but both predicted well.
Sites 1-4 compared to suburban site
When separate models were produced for the group of urban canyon sites and
the suburban site results similar to those for the combination of all sites were found.
The notable predictors were again UVA, UVB, and erythemal UV, while air pollution
and environmental measures were unimportant. However the difference between the
amount of variance predicted by the models for sites 1-4 was much less than that
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predicted by the models for the suburban site. Tables 25-28 show the results obtained
from these models. Tables 25 and 26 compare models produced for cholecalciferol
production at sites 1-4 and at the suburban site.
Linear regression model: Dependent variable cholecalciferol production at sites 1-4
Independent variables entered: UVB, UVA, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .592
UVA UVB Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta .194* .556* .149* -.109 .113* .049
Independent variables entered: Erythemal UV, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .865
Erythemal UV Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta .903* .055 -.043 .084* .067*
*Significant at .05 level or lower
Table 25: Linear regression model: Dependent variable cholecalciferol production at sites 1-4
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Linear regression model: Dependent variable cholecalciferol production at suburban site
Independent variables entered: UVB, UVA, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .927
UVA UVB Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta -.027 .961* .005 -.045 .055 -.065
Independent variables entered: Erythemal UV, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .960
Erythemal UV Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta .984* .037 -.128* -.036 .059*
*Significant at .05 level or lower
Table 26: Linear regression model: Dependent variable cholecalciferol production at suburban site.
This data shows that cholecalciferol production at the suburban site is modelled more
accurately than that in the urban canyon and that adding erythemal UV to the model
instead of the combination of UVA and UVB also produced more accurate models.
This second result is especially true for cholecalciferol production in the urban
canyon.
Tables 27 and 28 compare models describing the depletion of 7-DHC at the
urban canyon sites and at the suburban site.
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Linear regression model: Dependent variable 7-DHC depletion at sites 1-4
Independent variables entered: UVB, UVA, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .558
UVA UVB Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta .580* .181* .095 -.040 -.063 .115*
Independent variables entered: Erythemal UV, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .715
Erythemal UV Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta .840* .024 .035 -.047 .159*
*Significant at .05 level or lower
Table 27: Linear regression model: Dependent variable 7-DHC depletion at sites 1-4
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Linear regression model: Dependent variable 7-DHC depletion at suburban site
Independent variables entered: UVB, UVA, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .909
UVA UVB Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta .881* .092 .096 .053 -.209* -.153*
Independent variables entered: Erythemal UV, Pollution PM10, Visibility Reducing Particles, Temperature, Humidity
Variables excluded by model: None
R-squared value for model: .910
Erythemal UV Pollution PM-10
Visibility Reducing particles
Temperature Humidity
Standardized Beta .977* -.042 .207* -.240* -.085*
*Significant at .05 level or lower
Table 28: Linear regression model: Dependent variable 7-DHC depletion at suburban site
The results of these models of 7-DHC depletion are similar to those found by the
comparison between 7-DHC production models. The models predict suburban 7-
DHC depletion more accurately than urban canyon 7-DHC depletion and in the urban
canyon erythemal measurements predicted 7-DHC depletion much better than the
combination of UVA and UVB measurements.
In summary, these models show that overall, UVA associated with
measurements of 7-DHC depletion and UVB associated with measurements of
cholecalciferol production accurately during this study. However, at the urban
canyon locations erythemal UV was a better predictor for both cholecalciferol
production and 7-DHC depletion than either UVA or UVB. The measurements of
PM-10 particles, visibility reducing particles, temperature, and humidity did not have
a substantial impact on the prediction of either 7-DHC depletion or cholecalciferol
production. Finally, the models for the suburban site predicted both cholecalciferol
production and 7-DHC depletion with greater accuracy than those produced for the
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urban canyon sites. This suggests that there may have been some unmeasured factor/s
in the urban canyon environment influencing the outcome of the exposure of the
vitamin D dosimeter. Possibilities for further investigation are discussed in section
10.2.
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10. Discussion
10.1 Conclusions
With the use of observational measurements taken in the CBD and at a nearby
suburban site this study has clearly shown that during the winter of 2007 the urban
canyon area in Brisbane’s CBD received significantly less total UV, UVA,UVB, and
erythemal UV radiation than did the nearby suburban measurement site. Exposure of the
vitamin D dosimeter resulted in significantly less cholecalciferol production and 7-DHC
depletion at the urban canyon sites as well. During this study, measurements of UV
radiation correlated strongly with the production of cholecalciferol and the depletion of 7-
DHC from the vitamin D dosimeter.
Over the entire period of data collection (June 22 – August 30, 2007) the average
total UV received at the group of urban canyon sites (sites 1-4) was approximately 76%
less than the average total UV received at the suburban site. Similarly the average UVA
received at sites 1-4 was approximately 76% less than that received at the suburban site.
The average UVB received at sites 1-4 was approximately 67% less than that received at
the suburban site, a larger percentage than total UV and UVA. Although absolute
measures of UVB were greater at the suburban site, UVB made up a relatively larger
portion of total UV in the urban canyon than at the suburban site. The differences
between these respective urban canyon and suburban average values were all significant
with p-values less than 0.01. These results are very important, and show that the urban
canyon has the ability to reduce the amount of available unweighted total UV, as well as
the individual UVA and UVB bands.
When these results were further analysed it was found that the percentage of
suburban UV measured at sites 1-4 varied with respect to time of day. Morning and noon
measurements showed differences between urban canyon and suburban UV similar to
those described in the previous paragraph. During afternoon measurements sites 1-4
showed a greater percentage of suburban UV than did measurements taken during the
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morning or at noon. This result was explained by the fact that the solar zenith angles
associated with afternoon measurements were greater than those associated with morning
and noon measurements. These results agree with a Polish study suggesting that the
urban canyon environment can reduce the amount of UV radiation reaching the street
level [2].
The results of the analysis of erythemally-weighted UV data were similar to those
found for the unweighted data. When compared with the suburban site, the urban canyon
sites received significantly less erythemal UV. The average amount of erythemal UV
measured at sites 1-4 during this study was 0.095MED, while the average amount of
erythemal UV measured at the suburban site was more than four times greater at
0.375MED (p-value < 0.01). When erythemal UV data was analysed with respect to the
time of data collection it was found that the highest average amount of erythemal UV was
collected at noon both within the urban canyon and at the suburban location. The lowest
average erythemal UV values were found during the afternoon both at sites 1-4 and at the
suburban site. In addition, the average urban canyon erythemal UV measurement was
approximately 78% less than the average suburban measurement during both the morning
and noon collection periods. In the afternoon the average urban canyon erythemal UV
measurement was approximately 63% less than the average suburban measurement.
Again this is attributed to the greater solar zenith angles during afternoon measurements.
These findings mirror the results of the analysis of unweighted UV, and show that
erythemal UV was also affected by the urban canyon.
Data collected with the vitamin D dosimeter showed the urban canyon locations
to produce less cholecalciferol than the suburban site. The average amount of
cholecalciferol produced at sites 1-4 during this study was 0.128μg/mL, while at the
suburban site it was 0.536μg/mL (p-value < 0.01), approximately a 76% reduction in the
urban canyon. Stated another way, the average suburban value was over four times the
average urban canyon value. This is very striking and suggests that more investigation
into the health effects of UV exposure in the urban canyon is warranted.
Similar results were found with the analysis of data relating to 7-DHC depletion.
The average amount of 7-DHC depleted at sites 1-4 was 24.7μg/mL, while the average
amount of 7-DHC depleted at the suburban site was 77.7μg/mL (p-value < 0.01),
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approximately a 68% reduction in the urban canyon. In this case the suburban site saw
average 7-DHC depletion approximately three times greater than the urban canyon sites.
When vitamin D dosimeter data was analysed with respect to time of
measurement results coincided with those from the unweighted UV and erythemal UV
analyses. In terms of both cholecalciferol production and 7-DHC depletion there was a
greater difference between average urban canyon measurements and average suburban
site measurements collected during the morning and at noon than between those same
measurements collected in the afternoon. This disparity can be attributed to the same
difference in solar zenith angle that resulted in a closer relationship between suburban
and urban canyon UV levels during the afternoon data collection than during the morning
or noon collections. The public open space, while still receiving less UV and producing
less cholecalciferol than the suburban site, did significantly surpass values recorded at the
other urban canyon locations.
In addition to these findings, when vitamin D dosimeter measurements from the
urban canyon sites were matched with measurements from the suburban site taken at the
nearest date the difference between suburban and urban canyon data remained striking.
The average difference between the suburban measurements and matched urban
measurements was positive for all data collected at sites 1-4 (meaning that the suburban
site saw more cholecalciferol production and more 7-DHC depletion than the urban
canyon sites). The fact that such a distinct difference was found between urban canyon
measurements and suburban measurements shows that the UV radiation differences
measured between the two environments impacted directly on the production of
cholecalciferol and the depletion of 7-DHC within the vitamin D dosimeter.
These results suggest that the urban canyon environment may limit human
vitamin D production, which is what an Indian study measuring vitamin D status in
young children in conjunction with air pollution within an urban area also found [3]. The
implications of these findings are possibly very beneficial, as public health policy might
be improved by incorporating this information into messages which currently do not
make any distinction between UV exposure that takes place within the urban canyon or in
nearby suburban areas.
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The measurements of air pollution, temperature, and humidity did not display any
of the trends found in the previously discussed data. Air pollution measurements were
only collected at one location during this project, and this location was approximately
1km away from the urban canyon data collection sites and 3kms away from the suburban
collection site. Average measurements of air pollution (PM-10 particles) were greater
during times of data collection at the suburban site than during data collection times at
sites 1-4. During the entire study however, air pollution measurements did not reach
levels considered to be excessive by the National Environmental Protection Council. It is
unknown if measurements taken at each specific site would have provided different
results.
The absence of higher levels of air pollution associated with urban canyon
measurements and a lack of correlation with other variables make it difficult to come to
any conclusions regarding air pollution’s impact on the UV measurements and vitamin D
dosimeter exposures during this study. For these reasons the pollution measurements
from this project are viewed as inconclusive. However, previous research [15-17] has
linked air pollution to lower UV levels in urban environments, and this study does not
suggest otherwise.
Temperature and humidity measurements showed the suburban site to be
associated with a temperature of approximately 1°C greater than measurements from the
urban canyon. A small difference was found between average humidity associated with
urban canyon measurements and suburban measurements. Neither of these differences
was found to be significant however.
Measurements of UV radiation taken during this study correlated very well with
measurements of both cholecalciferol production and 7-DHC depletion. These
correlations occurred both when data collected at all sites was analysed together and
when data was separated between that collected at sites 1-4 and that collected at the
suburban site. Measurements taken at the suburban site correlated more highly with one
another than those taken in the urban canyon, however both showed very good
correlation. The correlations found during analysis show that measurements taken during
this project were of high quality and that the vitamin D dosimeter was accurately
capturing interactions between UV radiation and 7-DHC.
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Linear regression modelling predicted both cholecalciferol production and 7-DHC
depletion with a high degree of accuracy. Erythemal UV predicted both outcomes of
vitamin D dosimeter exposure slightly better than the combination of UVA and UVB
radiation. From the combination of UVA and UVB, UVB radiation was shown to predict
cholecalciferol production most accurately while UVA predicted 7-DHC depletion best.
When data was broken down according to urban canyon and suburban measurements
cholecalciferol production and 7-DHC depletion were both predicted best at the suburban
site. A possible explanation for this finding is that even though the erythemal action
spectrum does not directly relate to the production of cholecalciferol or the destruction of
7-DHC, it models those better than un-weighted UVA and UVB radiation.
In summary, this study has shown that the urban canyon environment can greatly
reduce the amount of UV radiation and vitamin D production from that of the nearby
suburban environment. Over the entire course of data collection the urban canyon
received an average of 24% of the cholecalciferol production that the suburban site
received. This difference is very striking considering these locations were approximately
2.5kms apart.
10.2 Limitations and future work
This study was conducted with the aim of collecting a large amount of data, and
while this was accomplished for sites 1-4, time restrictions made it impossible to collect
the same amount of data at site 5 (the public open space). Also, data was only collected
in one suburban location, which was a large field with a complete sky view. This
location obviously did not model all of the various environments that are found in
suburban areas. Future work can build upon this study by collecting data in more
locations in general, and specifically investigating UV radiation and vitamin D
production in public open spaces within the urban canyon and in a wider variety of
suburban locations.
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Linear regression models showed that the air pollution data collected during this
study did not predict production of cholecalciferol or depletion of 7-DHC as well for the
urban canyon sites as for the suburban location. This may be due to the inconclusiveness
of pollution measurements. As mentioned above pollution measurements were coming
from a single location. Future work in this area might focus directly on the aspect of air
pollution and its effect on human UV exposure in the urban canyon. Such study should
use a portable air pollution sensor to allow air pollution measurements to be taken at each
site in combination with the UV spectrometer and vitamin D dosimeter measurements.
It should be noted that the vitamin D dosimeter did not measure actual human
production of vitamin D, but rather in-vitro production. In-vitro measurement made it
possible to strip away many confounding factors such as skin colour, clothing selection,
and sun protection measures that influence an individual’s production of vitamin D,
which allowed for study of the basic environmental components of UV exposure in the
urban canyon. However, in-vivo measurements need to be taken to assess the actual
effect of urban canyon environment on human health as people will move between areas.
The development of a wearable in-vitro vitamin D dosimeter would be a very
good first step toward measuring actual in-vivo vitamin D production in different
environments. In addition, it may be interesting to recruit a cohort of volunteers who live
and work within the urban canyon and a second group who live and work in the suburbs
to wear erythemal UV dosimeters (which are currently used in many studies), so as to
compare the amount of erythemal UV received by people during daily activities in these
areas.
Finally, as this study has for the first time suggested large differences between the
urban canyon and nearby suburban environments, further data collection would add
weight to the results found during this project. This study was conducted during the
winter in Queensland, Australia, an environment that differs greatly to those found during
other seasons and at other locations. The summer months in Queensland are known for
extreme levels of UV radiation, and even with the impact of the urban canyon, UV levels
and vitamin D production may still be quite high in Brisbane’s CBD. However, urban
canyons located at higher latitudes may experience even lower UV levels and vitamin D
production throughout the year than observed during this study. How the urban canyon
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influences UV and vitamin D production in these situations is unknown, and the
collection of data during other times of the year and in other locations would help to
better quantify the impact of the urban canyon on human health in relation to UV
exposure.
10.3 Recommendations
This project has shown that levels of erythemal UV and vitamin D production can
vary greatly between suburban and nearby urban canyon environments – at times as
much as a 75% reduction in cholecalciferol production in the urban canyon was found.
These findings imply that exposure to UV radiation in these two areas may result in very
different outcomes. An exposure that leads to the production of a healthy amount of
vitamin D in a suburban area may result in little or no vitamin D production in an urban
canyon, even if the two locations are very close to one another. If one’s UV exposure
occurs mainly in the urban canyon vitamin D insufficiency or deficiency may result. On
the other hand, an exposure that is hazardous in a suburban setting may result in healthy
vitamin D production in a nearby urban canyon. Current sun exposure recommendations
for the general public, such as the UV index, do not reflect this however. These
recommendations make no distinction between the urban canyon environment and other
areas.
Skin types and personal UV exposure habits vary between individuals and the
most effective form of influencing public health in a positive manner is to educate people
so that they may make informed decisions regarding their personal sun safety and vitamin
D health. The knowledge that the urban canyon environment can influence UV radiation
and vitamin D production can form an important part of this education.
At this point, it may not be prudent to suggest changes to current sun safety
education policies, especially in an area such as Queensland, due to the extreme risk of
skin cancer. However, further study of UV radiation and vitamin D production in the
urban canyon is strongly suggested. This research could prove particularly beneficial in
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locations at higher latitude, because people spending significant amounts of time in urban
canyons at higher latitude may be at greater risk of vitamin D deficiency than previously
thought.
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