an estimation of canadian population exposure to cosmic rays from air travel
TRANSCRIPT
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ORIGINAL PAPER
An estimation of Canadian population exposure to cosmicrays from air travel
Jing Chen • Dustin Newton
Received: 8 August 2012 / Accepted: 28 October 2012 / Published online: 9 November 2012
� Her majesty the Queen in Right of Canada 2012
Abstract Based on air travel statistics in 1984, it was
estimated that less than 4 % of the population dose from
cosmic ray exposure would result from air travel. In the
present study, cosmic ray doses were calculated for more
than 3,000 flights departing from more than 200 Canadian
airports using actual flight profiles. Based on currently
available air travel statistics, the annual per capita effective
dose from air transportation is estimated to be 32 lSv for
Canadians, about 10 % of the average cosmic ray dose
received at ground level (310 lSv per year).
Keywords Cosmic rays � Annual effective dose �Population exposure
Introduction
Everyone is exposed to ionizing radiation from natural
sources. There are two main contributors to natural radia-
tion exposures: high-energy cosmic ray particles incident
on the Earth’s atmosphere and radioactive nuclides that
originate in the Earth’s crust and are present everywhere in
the environment. Background radiation levels in the atmo-
sphere are generated primarily by galactic cosmic rays.
There are two major effects that shield against primary
cosmic radiation, namely the Sun’s and the Earth’s mag-
netic fields. Entering the solar system, the fluence of cosmic
rays is modulated by the periodic solar activity: The Sun
emits a huge flow of matter known as solar wind which has
to be overcome by the primary particles (predominantly
protons). The intensity of the solar wind fluctuates
depending on solar activity, which can be deduced from the
number of sunspots, with a cycle of 11 years. The shielding
effect of the Sun is smaller during the period of solar
minimum activity. When approaching the Earth, the cosmic
rays are deflected by Earth’s magnetic field acting as cutoff
in their energy spectra. It is easiest to overcome this field at
the magnetic poles because the particles there run roughly
parallel to the magnetic field lines. In contrast, at the geo-
magnetic equator, the particles need to have much higher
energy (over 15 GeV) to cross perpendicularly the magnetic
field lines and enter the Earth’s atmosphere. Since the far
more frequent lower-energy particles are deflected away
from the Earth, radiation exposure is lower at the equator
than at the poles. Thus, the fluence of the primary particles
is a function of the time in the solar cycle and of the location
in the geomagnetic field. Interaction of these primary par-
ticles with the atoms in the atmosphere results in a complex
field of secondary cosmic radiation which for example
includes neutrons, protons, pions, photons, electrons, and
muons. A comprehensive review of worldwide exposure
from natural sources was given by the United Nations
Scientific Committee on the Effects of Atomic Radiation
(UNSCEAR) in its 2000 report (UNSCEAR 2000). It was
estimated that worldwide exposure to cosmic radiation
results in an average annual effective dose of 0.38 mSv.
This estimate is for exposure to cosmic rays at ground level
by applying the indoor shielding factor of 0.8 and assuming
indoor occupancy to be 80 % of time.
It is well understood that exposure to cosmic rays
increases strongly with altitude and somewhat less with
latitude. When traveling at commercial aircraft altitudes,
one could receive a significantly higher radiation dose than
that at sea level. In addition, the radiation exposure at a
given flight altitude increases two to three times from the
J. Chen (&) � D. Newton
Radiation Protection Bureau, Health Canada,
2720 Riverside Drive, Ottawa K1A 0K9, Canada
e-mail: [email protected]; [email protected]
123
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DOI 10.1007/s00411-012-0444-7
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equator to approximately 50� north or south. Thus, at high
altitude and latitudes close to the magnetic poles, such as
with some long-haul Canadian domestic and international
flights, radiation doses received during these flights would
be much higher than those received on short-haul flights at
lower altitudes and latitudes. In its report no. 94, the
National Council on Radiation Protection and Measure-
ments (NCRP) analyzed the exposure of the population in
the United States and Canada to cosmic rays, and estimated
that the average population effective dose from cosmic
radiation is 0.27 mSv per year; 0.26 mSv at ground with
consideration of altitude distribution of the population and
an additional 0.01 mSv from air travel (NCRP 1987).
Based on air travel statistics in 1984, the NCRP estimated
that less than 4 % of the population dose from cosmic ray
exposure would result from air travel.
Recently, a more accurate estimation of the exposure to
cosmic rays was conducted for more than 1500 commu-
nities across Canada (Chen et al. 2009). It was estimated
that the Canadian population-weighted average annual
effective dose due to cosmic ray exposure at ground level is
0.31 mSv, averaged over solar activity. Because the pop-
ulation-averaged occupancy time at aircraft altitudes would
only be several hours per year even with significantly
increasing air travel, the population dose from air trans-
portation is expected to remain a small fraction of that
resulting from cosmic ray exposure on the ground. In this
study, a more accurate estimation of radiation burden from
air traveling is made for the Canadian population based on
currently available air travel statistics. In addition to the
assessment of population doses from cosmic rays during air
travel, it is important to recognize that the range of indi-
vidual exposures is considerable. For radiation protection
of individual air travelers, average dose rates are also
estimated for typical Canadian domestic, transborder, and
international flights.
Methods
Estimation of doses to passengers is based on route doses
obtained from measurements or calculations of the effec-
tive dose rate as a function of flight parameters. There has
been considerable research carried out on both measure-
ment techniques and calculation methods, as summarized
in the report from the EURADOS WG5 (EC 2004). There
is general agreement between the results of experimental
determinations and computer calculations. The total
uncertainty in the values of effective dose calculated by the
different computing codes was estimated to be about 30 %,
and may extend up to 50 % if the calculations are based on
planned rather than actual flight profiles (EC 2004). The
uncertainties for the assessment of doses to air travelers
meet the accuracy requirements of the ICRP and ICRU
(ICRU 2010) when actual flight profiles are used. This
supports the approach of basing determinations of effective
dose for air travelers on the results of calculations.
There are several software packages that calculate
effective dose rates at aircraft altitudes and effective doses
to air crew or passengers, such as AVIDOS, EPCARD,
QARM, FREE, PCAIRE, and SIEVERT. The overall
agreement between the codes was generally better than
±20 % from the median (Bottollier-Depois et al. 2009). In
the present study, the software package, PCAIRE (Lewis
et al. 2005), was used. Based on over 160 in-flight mea-
surements, correlations have been developed to allow for
the interpolation of the cosmic ray dose rate for any global
position, altitude, and date. This resulted in a Predictive
Code for Aircrew Radiation Exposure (PCAIRE). The code
has been validated against the integral route dose mea-
surements made on 49 jet-altitude flights. On most flights,
the code agreed with the measured data (within 25 %). The
PCAIRE code was used online (www.pcaire.com) with
actual flight profiles available for all flights departing from
Canadian airports.
All departure flights were grouped into three categories:
domestic departures, US departures, and international
departures. With actual flight profiles available on the
Internet (details are given below), effective doses to pas-
sengers were calculated for each flight departing from a
Canadian airport. Canadian travel statistics with domestic,
transborder, and international flights were obtained from
Statistics Canada. In each category of air transportation, it
is assumed that the ratio of Canadian passengers to the total
passenger capacity applies to all flights in that category.
Assuming that all departure flights have the corre-
sponding flights arriving from the opposite direction, the
total number of flights is twice the number of departure
flights. Thus, the total population dose is twice the popu-
lation dose calculated for all flights departing from Cana-
dian airports.
Canadian airports and passenger capacities
A list of airports was taken from the commercial airports
directory provided by Wego.com (available at http://www.
wegotravel.ca/). Noticeably, absent from the list was Tor-
onto City Centre Airport (YTZ) and Arctic Bay Airport
(YAB), which were added for this study. The study list
contains a total of 259 airports in Canada. Each airport’s
Web site was visited and the departure information was
downloaded (airlines, flights, and destinations) for a single
day during the last 10 days of February 2011. In February
2011, a total of 211 airports were in operation with at least
one departure flight on the day when the Web site was
visited. For these 211 airports in Canada, there were 2,496
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domestic departures, 608 US departures, and 178 interna-
tional departures in a single day of February 2011.
It is well known that the number of flights varies sea-
sonally. Figure 1 shows the monthly variation of air carrier
movements for domestic, transborder, and international
movements in year 2011 reported by Statistics Canada
(2012a). Based on the statistics, the numbers of air carrier
movements in February are 6.8, 7.6, and 9.1 % for
domestic, transborder, and international, respectively. To
estimate the number of departures for any day in 2011, the
above obtained daily departure figures in February are,
therefore, adjusted by a factor of 1.128, 1.009, and 0.843
for domestic, transborder, and international departures,
respectively. Annual total numbers of departure flights are
the adjusted daily departure flights multiplied by 365 days,
as shown in Table 1.
For each departure flight, the airline Web site was vis-
ited, the aircraft type used for the flight was identified, and
the capacity of the given aircraft was recorded. This was
verified with individual airlines, because not every airline
has the same aircraft configurations even though the same
equipment was used. In Table 1, the information of pas-
senger capacities is the sum of the capacities from all
individual flights for different categories at individual air-
ports in various provinces.
Air travel statistics
The above estimation is the maximum passenger capacity
for air transportation in a year. To estimate effective doses
to Canadian passengers, air travel statistics for Canadians
are needed. A summary of the statistics is given in Table 2
(Statistics Canada 2012b). In 2010, Canadians traveled
22,709,807 times domestically by air, 6,971,307 times
across the border to the US, and 8,701,172 times to
countries other than the United States.
Actual flight profiles
In order to more accurately calculate the effective dose
received by a passenger during a given flight, actual flight
parameters are needed when using PCAIRE to calculate
effective doses received during flights. These parameters
are departure date, departing airport, arrival airport, ascent
time, descent time, flight altitude, and flight time. For aFig. 1 Monthly variation of the number of departing and arriving
flights for domestic, transborder, and international flights in 2011
Table 1 Departure information obtained from 211 airports in Canada in year 2011
Province Airports in
operation
Domestic departures US departures International departures
Flights Passenger
capacity
Flights Passenger
capacity
Flights Passenger
capacity
Alberta 10 392 28,880 65 6,692 14 2,863
British Columbia 29 401 26,118 71 8,014 24 5,865
Manitoba 14 152 7,362 17 1,038 2 378
New Brunswick 4 41 1,674 2 81 0 0
Newfoundland &
Labrador
20 125 4,806 5 583 2 222
Nova Scotia 3 79 5,321 21 1,055 3 569
Ontario 40 695 42,701 314 23,211 94 18,517
PEI 1 8 291 0 0 0 0
Quebec 43 355 18,431 104 8,083 37 8,317
Saskatchewan 2 57 4,786 9 534 2 272
Three Territories 45 191 7,877 0 0 0 0
Canada (daily, Feb) 211 2,496 14,8247 608 49,291 178 37,003
Canada (any day) 2,815 167,223 613 49,735 150 31,194
Canada (year 2011) 1,027,475 61,036,395 223,745 18,153,275 54,750 11,385,810
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given flight, the actual flight profile could vary to some
extent day by day. Since statistical results are averaged
over thousands of flights, daily variation of flight profiles
was ignored. Efforts were then focused on accurate esti-
mation of flight altitude, distance, and time.
Two Web sites were used to find all the flight infor-
mation needed to calculate the dose. The first site, Flight-
stats.com, provided all the flights departing each Canadian
airport on a given date. The total of 3,282 departure flights
from 211 Canadian airports was recorded on the Web site
for a given day in February 2011.
The data provided by Flightstats.com were not sufficient
for PCAIRE effective dose calculations. The second site,
Flightaware.com, provides real-time flight tracking. The
site provides flight information going back 7 days. After
7 days, users have to create an account, which provides
data as far back as 3 months. Each flight was searched on
this site, and data such as duration, equipment, speed,
altitude, and distance were recorded.
It is important to distinguish between direct and flown
distance. Direct distance is the distance between airports
while the distance flown is how many kilometers the air-
plane is in the air. If the flown distance is given, it was the
value recorded; otherwise, the direct distance was taken. In
most cases, the flown distances were recorded for calcu-
lating actual flight time.
Most flights on Flightaware.com include a track log
which includes the altitude and speed of the flight, updated
every minute. Using the track log, the ascent and descent
time of the flight can be determined. However, due to the
large number of flights being investigated in this study,
their ascent and descent times were not recorded individ-
ually. Instead, average ascent and descent times were cal-
culated for 10 flights in each of the 4 altitude ranges. The
averages used in the calculations are given in Table 3. A
constant flight altitude is then assumed after ascent and
before descent.
With actual flight profiles, radiation doses received by
passengers were calculated for all 3,282 flights departing
from Canadian airports in a day of February 2011.
Results and discussion
Among a total of 3,282 flights departing from Canadian
airports in a day of February 2011, flight profiles cannot be
found for some flights (\1 %) especially for very short
flights departing from airports in small communities. The
PCAIRE contains many airports in its database, but not all
of the 211 airports. Occasionally, the program cannot cal-
culate the effective dose between certain airports even
though the airport is in the database. In all those cases,
average effective doses obtained from similar flights
departing from nearby larger airports were assigned to the
flights with missing information.
Assuming the ratio of Canadian passengers to the total
passenger capacity applies to all flights in a given category
of air transportation, that is, 37.2 % for domestic, 38.4 %
for transborder, and 76.4 % for international flights (see
Table 2). Canadian annual collective dose is estimated to
be 1,076,748,198 lSv. Applying the Canadian population
of 34,126,200 in year 2010, the annual per capita effective
dose from air transportation is estimated to be 32 lSv. The
estimated annual per capita effective dose from air travel is
about 10 % of the average cosmic ray effective dose
received at ground level, which is 6 % higher than the
previous estimate made by the NCRP in 1984 (NCRP
1987). This increase is likely due to significantly increased
air travel in the past decades.
Detailed results for different categories are given in
Table 4 together with air travel statistics and estimates for
the year 2010. One can see clearly in Table 4 that more
than half of the estimated population dose due to air
transportation results from international flights.
The per capita annual effective dose is averaged over
entire populations, including non-exposed individuals.
Everyone is exposed to some level of background radiation
at ground level depending on where they live. Therefore,
for background exposure, the per capita annual effective
dose is the dose received more or less by all individuals. In
the case of air transportation, the per capita annual effec-
tive dose provides a broad indication of population expo-
sure to cosmic rays when traveling by air. However,
significant variations exist in the patterns of exposure
received by individuals. Some individuals might have
Table 2 Statistics of air travel (enplaned or deplaned) in Canada
Domestic Transborder International
Total annual capacity by
all carriers
61,036,395 18,153,275 11,385,810
All Canadian passengers
in 2010
22,709,807a 6,971,307 8,701,172
Ratio of Canadian
passengers to the
capacity
0.372 0.384 0.764
a Private communication from Don Kirkpatrick, Aviation Statistics
Centre, Statistics Canada, July 26, 2011
Table 3 Average ascent and descent time for flights at various alti-
tude ranges
Altitude (ft) Ascent time
(min)
Descent time
(min)
C35000 25 25
25,000–34,999 20 20
15,000–24,999 15 16
\ 15,000 9 10
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multiple trips, while others might have none in a year or
none at all in their lifetime. For the purpose of radiation
protection to individuals, dose rates in the units of lSv/h
were derived for different flight durations averaged over
more than a thousand flights departing from the three
largest Canadian airports (Toronto, Vancouver, and Mon-
treal). Resulting information is summarized in Table 5.
It is well known that cosmic ray dose rates to which aircraft
passengers are exposed increase significantly with the alti-
tude. The doses to passengers depend on flight altitude and
flight time at the altitude. Short flights with durations less than
30 min normally have scheduled altitudes less than 10,000
feet, and actually only have a few minutes cruising at the
scheduled altitude. On average, the dose rate in these very
short flights is 0.4 lSv/h. Flights with longer flight time are
normally scheduled to fly between 18,000 and 38,000 feet,
and they also have longer time cruising at the scheduled
altitude. For most international flights ([3 h), the average
dose rate is 5.5 lSv/h. Based on the information given in
Table 5, individuals can estimate cosmic ray doses received
during a given flight. For example, for a traveler taking a flight
from Ottawa to Vancouver for 318 min (5.3 h), the cosmic
ray dose can be estimated as 5.5 lSv/h 9 5.3 h = 29 lSv.
This is only 1.2 % of the worldwide average annual exposure
from natural sources (2.4 mSv) (UNSCEAR 2000). How-
ever, if an individual made 10 round trips between Toronto
and Frankfurt in a year, the annual effective dose due to air
travel could be 0.8 mSv (10 9 2 9 5.5 lSv/h 9 7.2 h =
0.8 mSv), comparable to the public annual dose limit of
1 mSv recommended by the ICRP. For someone who had 40
round trips between Toronto and Hong Kong in a year, such as
the air crew, the annual effective dose could be as high as
6.6 mSv (40 9 2 9 5.5 lSv/h 9 15 h = 6.6 mSv).
It should be mentioned that the result of Canadian popu-
lation exposure to cosmic rays from air travel is an estimate
using air travel statistics in year 2010 and flight information in
2011. Based on the US National Aeronautics and Space
Administration (NASA 2012), solar activity in 2011 was
medium between the solar minimum and maximum. The
estimated population exposure to cosmic rays from air travel
is the value roughly averaged over solar activity. At aircraft
altitude, it is well known that the effective doses can differ up
to tens of percent between solar minimum and solar maxi-
mum,especially fora regionwith lowergeomagnetic rigidity,
such as Canada. The influence of solar activity can be much
more significant for individual flights when assessing indi-
vidual’s effective dose received from a given flight at a given
time. In case of solar particle events, although these events are
rare, the solar events can cause a significant increase in the
effective dose obtained during air traveling.
Conclusions
Based on currently available air travel statistics, the annual
per capita effective dose from air transportation is esti-
mated to be 32 lSv for Canadians, about 10 % of the
average cosmic ray dose received at ground level (310 lSv
per year). While the dose received during air travel will
depend on the number and length of flights, for an average
traveler, the health impact from cosmic radiation exposure
is trivial. For someone who takes many long-haul flights
per year, such as air crew, the annual radiation dose could
approach a few times the dose received from natural
background radiation at ground.
References
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Flight duration Flight altitude (ft) Dose rate (lSv/h)
\30 min 9,300 ± 3700 0.4 ± 0.3
0.5–1 h 24,400 ± 8400 1.4 ± 0.8
1–3 h 31,100 ± 6700 3.5 ± 1.8
[3 h 35,400 ± 2400 5.5 ± 1.2
Table 4 Results of Canadian population dose (effective dose) received from traveling by air together with some travel statistics
Domestic Transborder International Total
Estimated annual departure flights 1,027,475 223,745 54,750 1,305,970
Estimated annual passenger capacity 61,036,395 18,153,275 11,385,810 90,575,480
Canadian air travelers in 2010 22,709,807 6,971,307 8,701,172 38,382,286
Ratio of Canadian passengers to the total passenger capacity 0.372 0.384 0.764
Canadian annual collective dose (round trips) (lSv) 315,595,536 162,699,455 598,453,207 1,076,748,198
Annual effective dose per capitaa (lSv) 9.3 4.8 17.5 31.5
Ratio to effective dose at ground level 0.030 0.015 0.057 0.102
a Using Canadian population of 34,126,200 in 2010 (Statistics Canada 2011)
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