global environmental issues- anuja joshi

8/9/2019 Global Environmental Issues- Anuja Joshi

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A

PROJECT REPORT

ON

GLOBAL ENVIRONMENTAL ISSUES

SUBMITTED IN PARTIAL FULFILLMENT FOR THE AWARD OF DEGREE OF

MASTER OF SCIENCE (M.Sc.)

(INDIAN INSTITUTE OF ECOLOGY AND ENVIRONMENT

SIKKIM-MANIPAL UNIVERSITY, DELHI)

2008-10

BY

RANJANA G. DESHPANDE

ROLL NO. 810832241


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CHAPTER 1

OZONE DEPLETION

INTRODUCTION

The ozone layer protects the Earth from the ultraviolet rays sent down by the sun. If the

ozone layer is depleted by human action, the effects on the planet could be

catastrophic.

Ozone is present in the stratosphere. The stratosphere reaches 30 miles above the

Earth, and at the very top it contains ozone. The suns rays are absorbed by the ozone

in the stratosphere and thus do not reach the Earth

Ozone is a bluish gas that is formed by three atoms of oxygen. The form of oxygen that

humans breathe in consists of two oxygen atoms, O2. When found on the surface of the

planet, ozone is considered a dangerous pollutant and is one substance responsible for

producing the greenhouse effect.The highest regions of the stratosphere contain about

90% of all ozone.

In recent years, the ozone layer has been the subject of much discussion. And rightlyso, because the ozone layer protects both plant and animal life on the planet. The fact

that the ozone layer was being depleted was discovered in the mid-1980s. The main

cause of this is the release of CFCs, chlorofluorocarbons.

Antarctica was an early victim of ozone destruction. A massive hole in the ozone layer

right above Antarctica now threatens not only that continent, but many others that could

be the victims of Antarctica's melting icecaps. In the future, the ozone problem will have

to be solved so that the protective layer can be conserved.


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about 10 to 50 km (32,000 to 164,000 feet) above Earth's surface. About 90% of the

ozone in our atmosphere is contained in the stratosphere. Ozone concentrations are

greatest between about 20 and 40 km, where they range from about 2 to 8 parts per

million. If all of the ozone were compressed to the pressure of the air at sea level, it

would be only a few millimeters thick.

Structure

The structure of ozone, according to experimental evidence from microwave

spectroscopy, is bent, with C2v symmetry (similar to the water molecule), O O distance

of 127.2 pm and O O O angle of 116.78. The central atom forms an sp

hybridization with one lone pair. Ozone is a polar molecule with a dipole moment of

0.5337 D. The bonding can be expressed as a resonance hybrid with a single bond on

one side and double bond on the other producing an overall bond order of 1.5 for each

side.

Chemistry

Ozone is a powerful oxidizing agent, far better than dioxygen. It is also unstable at high

concentrations, decaying to ordinary diatomic oxygen (in about half an hour in

atmospheric conditions):

2 O3 3 O2

This reaction proceeds more rapidly with increasing temperature and decreasing

pressure. Deflagration of ozone can be triggered by a spark, and can occur in ozone

concentrations of 10 wt% or higher.


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Ozone layer

The ozone layer is a layer in Earth's atmosphere which contains relatively high

concentrations of ozone (O3). This layer absorbs 93-99% of the sun's high frequency

ultraviolet light, which is potentially damaging to life on earth. Over 91% of the ozone in

Earth's atmosphere is present here. It is mainly located in the lower portion of the

stratosphere from approximately 10 km to 50 km above Earth, though the thickness

varies seasonally and geographically. The ozone layer was discovered in 1913 by the

French physicists Charles Fabry and Henri Buisson. Its properties were explored in

detail by the British meteorologist G. M. B. Dobson, who developed a simple

spectrophotometer (the Dobsonmeter) that could be used to measure stratospheric

ozone from the ground. Between 1928 and 1958 Dobson established a worldwidenetwork of ozone monitoring stations which continues to operate today. The "Dobson

unit", a convenient measure of the columnar density of ozone overhead, is named in his

honor.

Ultraviolet light and ozone


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Levels of ozone at various altitudes and blocking of ultraviolet radiation.

UV-B energy levels at several altitudes. Blue line shows DNA sensitivity. Red line

shows surface energy level with 10% decrease in ozone

Although the concentration of the ozone in the ozone layer is very small, it is vitally

important to life because it absorbs biologically harmful ultraviolet (UV) radiation coming

from the Sun. UV radiation is divided into three categories, based on its wavelength;

these are referred to as UV-A (400-315 nm), UV-B (315-280 nm), and UV-C (280-

100 nm). UV-C, which would be very harmful to humans, is entirely screened out by

ozone at around 35 km altitude. UV-B radiation can be harmful to the skin and is the

main cause of sunburn; excessive exposure can also cause genetic damage, resulting

in problems such as skin cancer. The ozone layer is very effective at screening out UV-

B; for radiation with a wavelength of 290 nm, the intensity at the top of the atmosphere

is 350 million times stronger than at the Earth's surface. Nevertheless, some UV-B

reaches the surface. Most UV-A reaches the surface; this radiation is significantly less

harmful, although it can potentially cause genetic damage.


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Distribution of ozone in the stratosphere

The thickness of the ozone layer that is, the total amount of ozone in a column

overhead varies by a large factor worldwide, being in general smaller near the equator

and larger towards the poles. It also varies with season, being in general thicker during

the spring and thinner during the autumn in the northern hemisphere. The reasons for

this latitude and seasonal dependence are complicated, involving atmospheric

circulation patterns as well as solar intensity.

Since stratospheric ozone is produced by solar UV radiation, one might expect to find

the highest ozone levels over the tropics and the lowest over polar regions. The same

argument would lead one to expect the highest ozone levels in the summer and the

lowest in the winter. The observed behavior is very different: most of the ozone is found

in the mid-to-high latitudes of the northern and southern hemispheres, and the highest

levels are found in the spring, not summer, and the lowest in the autumn, not winter in

the northern hemisphere. During winter, the ozone layer actually increases in depth.

This puzzle is explained by the prevailing stratospheric wind patterns, known as the

Brewer-Dobson circulation. While most of the ozone is indeed created over the tropics,

the stratospheric circulation then transports it poleward and downward to the lower

stratosphere of the high latitudes. However in the southern hemisphere, owing to the

ozone hole phenomenon, the lowest amounts of column ozone found anywhere in the

world are over the Antarctic in the southern spring period of September and October.

Ozone as a greenhouse gas

Although ozone was present at ground level before the Industrial Revolution, peak

concentrations are now far higher than the pre-industrial levels, and even background

concentrations well away from sources of pollution are substantially higher. This

increase in ozone is of further concern because ozone present in the upper troposphere

acts as a greenhouse gas, absorbing some of the infrared energy emitted by the earth.

Quantifying the greenhouse gas potency of ozone is difficult because it is not present in

uniform concentrations across the globe. However, the scientific review on the climate


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change (the IPCC Third Assessment Report) suggests that the radiative forcing of

tropospheric ozone is about 25% that of carbon dioxide.

Ozone depletion

Ozone depletion describes two distinct, but related observations: a slow, steady decline

of about 4% per decade in the total volume of ozone in Earth's stratosphere (ozone

layer) since the late 1970s, and a much larger, but seasonal, decrease in stratospheric

ozone over Earth's polar regions during the same period. The latter phenomenon is

commonly referred to as the ozone hole. In addition to this well-known stratospheric

ozone depletion, there are also tropospheric ozone depletion events, which occur near

the surface in polar regions during spring.

Image of the largest Antarctic ozone hole ever recorded (September 2006).

The detailed mechanism by which the polar ozone holes form is different from that for

the mid-latitude thinning, but the most important process in both trends is catalytic

destruction of ozone by atomic chlorine and bromine. The main source of these halogen


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atoms in the stratosphere is photodissociation of chlorofluorocarbon (CFC) compounds,

commonly called freons, and of bromofluorocarbon compounds known as halons.

These compounds are transported into the stratosphere after being emitted at the

surface. Both ozone depletion mechanisms strengthened as emissions of CFCs and

halons increased.

CFCs and other contributory substances are commonly referred to as ozone-depleting

substances (ODS). Since the ozone layer prevents most harmful UVB wavelengths

(270315 nm) of ultraviolet light (UV light) from passing through the Earth's atmosphere,

observed and projected decreases in ozone have generated worldwide concern leading

to adoption of the Montreal Protocol that bans the production of CFCs and halons as

well as related ozone depleting chemicals such as carbon tetrachloride andtrichloroethane. It is suspected that a variety of biological consequences such as

increases in skin cancer, cataracts, damage to plants, and reduction of plankton

populations in the ocean's photic zone may result from the increased UV exposure due

to ozone depletion

Ozone cycle overview

Three forms (or allotropes) of oxygen are involved in the ozone-oxygen cycle: oxygenatoms (O or atomic oxygen), oxygen gas (O2 or diatomic oxygen), and ozone gas (O3 or

triatomic oxygen). Ozone is formed in the stratosphere when oxygen molecules

photodissociate after absorbing an ultraviolet photon whose wavelength is shorter than

240 nm. This produces two oxygen atoms. The atomic oxygen then combines with O2 to

create O3. Ozone molecules absorb UV light between 310 and 200 nm, following which

ozone splits into a molecule of O2 and an oxygen atom. The oxygen atom then joins up

with an oxygen molecule to regenerate ozone. This is a continuing process which

terminates when an oxygen atom "recombines" with an ozone molecule to make two O2

molecules: O + O3 2 O2


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Global monthly average total ozone amount.

The overall amount of ozone in the stratosphere is determined by a balance between

photochemical production and recombination.

Ozone can be destroyed by a number of free radical catalysts, the most important of

which are the hydroxyl radical (OH), the nitric oxide radical (NO), atomic chlorine (Cl)

and bromine (Br). All of these have both natural and manmade sources; at the present

time, most of the OH and NO in the stratosphere is of natural origin, but human activity

has dramatically increased the levels of chlorine and bromine. These elements are

found in certain stable organic compounds, especially chlorofluorocarbons (CFCs),

which may find their way to the stratosphere without being destroyed in the troposphere

due to their low reactivity. Once in the stratosphere, the Cl and Br atoms are liberated

from the parent compounds by the action of ultraviolet light, e.g. ('h' is Planck's

constant, '' is frequency of electromagnetic radiation)

CFCl3 + h CFCl2 + Cl

The Cl and Br atoms can then destroy ozone molecules through a variety of catalytic

cycles. In the simplest example of such a cycle, a chlorine atom reacts with an ozone


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molecule, taking an oxygen atom with it (forming ClO) and leaving a normal oxygen

molecule. The chlorine monoxide (i.e., the ClO) can react with a second molecule of

ozone (i.e., O3) to yield another chlorine atom and two molecules of oxygen. The

chemical shorthand for these gas-phase reactions is:

Cl + O3 ClO + O2

ClO + O3 Cl + 2 O2

The overall effect is a decrease in the amount of ozone. More complicated mechanisms

have been discovered that lead to ozone destruction in the lower stratosphere as well.

A single chlorine atom would keep on destroying ozone (thus a catalyst) for up to twoyears (the time scale for transport back down to the troposphere) were it not for

reactions that remove them from this cycle by forming reservoir species such as

hydrogen chloride (HCl) and chlorine nitrate (ClONO2). On a per atom basis, bromine is

even more efficient than chlorine at destroying ozone, but there is much less bromine in

the atmosphere at present. As a result, both chlorine and bromine contribute

significantly to the overall ozone depletion. Laboratory studies have shown that fluorine

and iodine atoms participate in analogous catalytic cycles. However, in the Earth's

stratosphere, fluorine atoms react rapidly with water and methane to form strongly-

bound HF, while organic molecules which contain iodine react so rapidly in the lower

atmosphere that they do not reach the stratosphere in significant quantities.

Furthermore, a single chlorine atom is able to react with 100,000 ozone molecules. This

fact plus the amount of chlorine released into the atmosphere by chlorofluorocarbons

(CFCs) yearly demonstrates how dangerous CFCs are to the environment.

OZONE DEPLETION CAUSES:

Only a few factors combine to create the problem of ozone layer depletion. The

production and emission of CFCs, chlorofluorocarbons, is by far the leading cause.


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Many countries have called for the end of CFC production because only a few produce

the chemical. However, those industries that do use CFCs do not want to discontinue

usage of this highly valuable industrial chemical.

CFCs are used in industry in a variety of ways and have been amazingly useful in many

products. Discovered in the 1930s by American chemist Thomas Midgley, CFCs came

to be used in refrigerators, home insulation, plastic foam, and throwaway food

containers.

Only later did people realize the disaster CFCs caused in the stratosphere. There, the

chlorine atom is removed from the CFC and attracts one of the three oxygen atoms in

the ozone molecule. The process continues, and a single chlorine atom can destroy

over 100,000 molecules of ozone.

In 1974, Sherwood Rowland and Mario Molina followed the path of CFCs. Their

research proved that CFCs were entering the atmosphere, and they concluded that

99% of all CFC molecules would end up in the stratosphere.

Only in 1984, when the ozone layer hole was discovered over Antarctica, was the proof

truly conclusive. At that point, it was hard to question the destructive capabilities of

CFCs.

Even if CFCs were banned, problems would remain. There would still be no way to

remove the CFCs that are now present in the environment. Clearly though, something

must be done to limit this international problem in the future

Observations on ozone layer depletion

The most pronounced decrease in ozone has been in the lower stratosphere. However,

the ozone hole is most usually measured not in terms of ozone concentrations at these

levels (which are typically of a few parts per million) but by reduction in the total column

ozone, above a point on the Earth's surface, which is normally expressed in Dobson

units, abbreviated as "DU". Marked decreases in column ozone in the Antarctic spring


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and early summer compared to the early 1970s and before have been observed using

instruments such as the Total Ozone Mapping Spectrometer (TOMS).

Lowest value of ozone measured by TOMS each year in the ozone hole.

Reductions of up to 70% in the ozone column observed in the austral (southern

hemispheric) spring over Antarctica and first reported in 1985 (Farman et al. 1985) are

continuing. Through the 1990s, total column ozone in September and October have

continued to be 4050% lower than pre-ozone-hole values. In the Arctic the amount lost

is more variable year-to-year than in the Antarctic. The greatest declines, up to 30%,

are in the winter and spring, when the stratosphere is colder.

Reactions that take place on polar stratospheric clouds (PSCs) play an important role in

enhancing ozone depletion. PSCs form more readily in the extreme cold of Antarcticstratosphere. This is why ozone holes first formed, and are deeper, over Antarctica.

Early models failed to take PSCs into account and predicted a gradual global depletion,

which is why the sudden Antarctic ozone hole was such a surprise to many scientists.


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In middle latitudes it is preferable to speak of ozone depletion rather than holes.

Declines are about 3% below pre-1980 values for 3560N and about 6% for 3560S.

In the tropics, there are no significant trends. ]

Ozone depletion also explains much of the observed reduction in stratospheric and

upper tropospheric temperatures. The source of the warmth of the stratosphere is the

absorption of UV radiation by ozone, hence reduced ozone leads to cooling. Some

stratospheric cooling is also predicted from increases in greenhouse gases such as

CO2; however the ozone-induced cooling appears to be dominant.

Predictions of ozone levels remain difficult. The World Meteorological Organization

Global Ozone Research and Monitoring Project - Report No. 44 comes out strongly in

favor for the Montreal Protocol, but notes that a UNEP 1994 Assessment overestimated

ozone loss for the 19941997 period

Chemicals in the atmosphere

CFCs in the atmosphere

Chlorofluorocarbons (CFCs) were invented by Thomas Midgley in the 1920s. They were

used in air conditioning/cooling units, as aerosol spray propellants prior to the 1980s,and in the cleaning processes of delicate electronic equipment. They also occur as by-

products of some chemical processes. No significant natural sources have ever been

identified for these compounds their presence in the atmosphere is due almost

entirely to human manufacture. As mentioned in the ozone cycle overview above, when

such ozone-depleting chemicals reach the stratosphere, they are dissociated by

ultraviolet light to release chlorine atoms. The chlorine atoms act as a catalyst, and

each can break down tens of thousands of ozone molecules before being removed from

the stratosphere. Given the longevity of CFC molecules, recovery times are measured

in decades. It is calculated that a CFC molecule takes an average of 15 years to go

from the ground level up to the upper atmosphere, and it can stay there for about a

century, destroying up to one hundred thousand ozone molecules during that time.


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Verification of observations

Scientists have been increasingly able to attribute the observed ozone depletion to the

increase of man-made (anthropogenic) halogen compounds from CFCs by the use of

complex chemistry transport models and their validation against observational data (e.g.

SLIMCAT, CLaMS). These models work by combining satellite measurements of

chemical concentrations and meteorological fields with chemical reaction rate constants

obtained in lab experiments. They are able to identify not only the key chemical

reactions but also the transport processes which bring CFC photolysis products into

contact with ozone

The ozone hole and its causes

Ozone hole in North America during 1984 (abnormally warm reducing ozone depletion)

and 1997 (abnormally cold resulting in increased seasonal depletion).


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The Antarctic ozone hole is an area of the Antarctic stratosphere in which the recent

ozone levels have dropped to as low as 33% of their pre-1975 values. The ozone hole

occurs during the Antarctic spring, from September to early December, as strong

westerly winds start to circulate around the continent and create an atmospheric

container. Within this polar vortex, over 50% of the lower stratospheric ozone is

destroyed during the Antarctic spring.

As explained above, the primary cause of ozone depletion is the presence of chlorine-

containing source gases (primarily CFCs and related halocarbons). In the presence of

UV light, these gases dissociate, releasing chlorine atoms, which then go on to catalyze

ozone destruction. The Cl-catalyzed ozone depletion can take place in the gas phase,

but it is dramatically enhanced in the presence of polar stratospheric clouds (PSCs).

These polar stratospheric clouds form during winter, in the extreme cold. Polar winters

are dark, consisting of 3 months without solar radiation (sunlight). The lack of sunlight

contributes to a decrease in temperature and the polar vortex traps and chills air.

Temperatures hover around or below -80 C. These low temperatures form cloud

particles and are composed of either nitric acid (Type I PSC) or ice (Type II PSC). Both

types provide surfaces for chemical reactions that lead to ozone destruction.

The photochemical processes involved are complex but well understood. The key

observation is that, ordinarily, most of the chlorine in the stratosphere resides in stable

"reservoir" compounds, primarily hydrochloric acid (HCl) and chlorine nitrate (ClONO2).

During the Antarctic winter and spring, however, reactions on the surface of the polar

stratospheric cloud particles convert these "reservoir" compounds into reactive free

radicals (Cl and ClO). The clouds can also remove NO2 from the atmosphere by

converting it to nitric acid, which prevents the newly formed ClO from being converted

back into ClONO2.

The role of sunlight in ozone depletion is the reason why the Antarctic ozone depletion

is greatest during spring. During winter, even though PSCs are at their most abundant,

there is no light over the pole to drive the chemical reactions. During the spring,


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however, the sun comes out, providing energy to drive photochemical reactions, and

melt the polar stratospheric clouds, releasing the trapped compounds.]

Most of the ozone that is destroyed is in the lower stratosphere, in contrast to the much

smaller ozone depletion through homogeneous gas phase reactions, which occurs

primarily in the upper stratosphere.

Warming temperatures near the end of spring break up the vortex around mid-

December. As warm, ozone-rich air flows in from lower latitudes, the PSCs are

destroyed, the ozone depletion process shuts down, and the ozone hole closes.

Consequences of ozone layer depletion

Since the ozone layer absorbs UVB ultraviolet light from the Sun, ozone layer depletion

is expected to increase surface UVB levels, which could lead to damage, including

increases in skin cancer. This was the reason for the Montreal Protocol. Although

decreases in stratospheric ozone are well-tied to CFCs and there are good theoretical

reasons to believe that decreases in ozone will lead to increases in surface UVB, there

is no direct observational evidence linking ozone depletion to higher incidence of skin

cancer in human beings. This is partly due to the fact that UVA, which has also been

implicated in some forms of skin cancer, is not absorbed by ozone, and it is nearly

impossible to control statistics for lifestyle changes in the populace

Increased UV

Ozone, while a minority constituent in the Earth's atmosphere, is responsible for most of

the absorption of UVB radiation. The amount of UVB radiation that penetrates through

the ozone layer decreases exponentially with the slant-path thickness/density of the

layer. Correspondingly, a decrease in atmospheric ozone is expected to give rise to

significantly increased levels of UVB near the surface.

Increases in surface UVB due to the ozone hole can be partially inferred by radiative

transfer model calculations, but cannot be calculated from direct measurements


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because of the lack of reliable historical (pre-ozone-hole) surface UV data, although

more recent surface UV observation measurement programmes exist (e.g. at Lauder,

New Zealand).

Because it is this same UV radiation that creates ozone in the ozone layer from O2

(regular oxygen) in the first place, a reduction in stratospheric ozone would actually tend

to increase photochemical production of ozone at lower levels (in the troposphere),

although the overall observed trends in total column ozone still show a decrease, largely

because ozone produced lower down has a naturally shorter photochemical lifetime, so

it is destroyed before the concentrations could reach a level which would compensate

for the ozone reduction higher up.

Ozone depletion effects:

y Even minor problems of ozone depletion can have major effects. Every time

even a small amount of the ozone layer is lost, more ultraviolet light from the sun

can reach the Earth.

y Every time 1% of the ozone layer is depleted, 2% more UV-B is able to reach the

surface of the planet. UV-B increase is one of the most harmful consequences of

ozone depletion because it can cause skin cancer.y The increased cancer levels caused by exposure to this ultraviolet light could be

enormous. The EPA estimates that 60 million Americans born by the year 2075

will get skin cancer because of ozone depletion. About one million of these

people will die.

y In addition to cancer, some research shows that a decreased ozone layer will

increase rates of malaria and other infectious diseases. According to the EPA,

17 million more cases of cataracts can also be expected.

y The environment will also be negatively affected by ozone depletion. The life

cycles of plants will change, disrupting the food chain. Effects on animals will

also be severe, and are very difficult to foresee.


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y Oceans will be hit hard as well. The most basic microscopic organisms such as

plankton may not be able to survive. If that happened, it would mean that all of

the other animals that are above plankton in the food chain would also die out.

Other ecosystems such as forests and deserts will also be harmed.

y The planet's climate could also be affected by depletion of the ozone layer. Wind

patterns could change, resulting in climatic changes throughout the world.

Biological effects

The main public concern regarding the ozone hole has been the effects of of increased

surface UV and microwave radiation on human health. So far, ozone depletion in most

locations has been typically a few percent and, as noted above, no direct evidence of

health damage is available in most latitudes. Were the high levels of depletion seen in

the ozone hole ever to be common across the globe, the effects could be substantially

more dramatic. As the ozone hole over Antarctica has in some instances grown so large

as to reach southern parts of Australia and New Zealand, environmentalists have been

concerned that the increase in surface UV could be significant.

Effects on humans

UVB (the higher energy UV radiation absorbed by ozone) is generally accepted to be a

contributory factor to skin cancer. In addition, increased surface UV leads to increased

tropospheric ozone, which is a health risk to humans. The increased surface UV also

represents an increase in the vitamin D synthetic capacity of the sunlight.

The cancer preventive effects of vitamin D represent a possible beneficial effect of

ozone depletion. In terms of health costs, the possible benefits of increased UV

irradiance may outweigh the burden.

1. Basal and Squamous Cell Carcinomas -- The most common forms of skin cancer

in humans, basal and squamous cell carcinomas, have been strongly linked to UVB

exposure. The mechanism by which UVB induces these cancers is well understood


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absorption of UVB radiation causes the pyrimidine bases in the DNA molecule to form

dimers, resulting in transcription errors when the DNA replicates. These cancers are

relatively mild and rarely fatal, although the treatment of squamous cell carcinoma

sometimes requires extensive reconstructive surgery. By combining epidemiological

data with results of animal studies, scientists have estimated that a one percent

decrease in stratospheric ozone would increase the incidence of these cancers by 2%.

2. Malignant Melanoma -- Another form of skin cancer, malignant melanoma, is much

less common but far more dangerous, being lethal in about 15% - 20% of the cases

diagnosed. The relationship between malignant melanoma and ultraviolet exposure is

not yet well understood, but it appears that both UVB and UVA are involved.

Experiments on fish suggest that 90 to 95% of malignant melanomas may be due toUVA and visible radiation whereas experiments on opossums suggest a larger role for

UVB. Because of this uncertainty, it is difficult to estimate the impact of ozone depletion

on melanoma incidence. One study showed that a 10% increase in UVB radiation was

associated with a 19% increase in melanomas for men and 16% for women. A study of

people in Punta Arenas, at the southern tip of Chile, showed a 56% increase in

melanoma and a 46% increase in nonmelanoma skin cancer over a period of seven

years, along with decreased ozone and increased UVB levels.

3. Cortical Cataracts -- Studies are suggestive of an association between ocular

cortical cataracts and UV-B exposure, using crude approximations of exposure and

various cataract assessment techniques. A detailed assessment of ocular exposure to

UV-B was carried out in a study on Chesapeake Bay Watermen, where increases in

average annual ocular exposure were associated with increasing risk of cortical opacity.

In this highly exposed group of predominantly white males, the evidence linking cortical

opacities to sunlight exposure was the strongest to date. However, subsequent data

from a population-based study in Beaver Dam, WI suggested the risk may be confined

to men. In the Beaver Dam study, the exposures among women were lower than

exposures among men, and no association was seen. Moreover, there were no data

linking sunlight exposure to risk of cataract in African Americans, although other eye


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diseases have different prevalences among the different racial groups, and cortical

opacity appears to be higher in African Americans compared with whites.

4. Increased Tropospheric Ozone -- Increased surface UV leads to increased

tropospheric ozone. Ground-level ozone is generally recognized to be a health risk, as

ozone is toxic due to its strong oxidant properties. At this time, ozone at ground level is

produced mainly by the action of UV radiation on combustion gases from vehicle

exhausts.

Effects on crops

An increase of UV radiation would be expected to affect crops. A number of

economically important species of plants, such as rice, depend on cyanobacteria

residing on their roots for the retention of nitrogen. Cyanobacteria are sensitive to UV

light and they would be affected by its increase.

Ozone depletion and global warming

Although they are often interlinked in the mass media, the connection between global

warming and ozone depletion is not strong. There are five areas of linkage:

Radiative forcing from various greenhouse gases and other sources.

y The same CO2 radiative forcing that produces near-surface global warming is

expected to cool the stratosphere. This cooling, in turn, is expected to produce a

relative increase in polar ozone (O3) depletion and the frequency of ozone holes.

y Conversely, ozone depletion represents a radiative forcing of the climate system.

There are two opposing effects: Reduced ozone causes the stratosphere to

absorb less solar radiation, thus cooling the stratosphere while warming the

troposphere; the resulting colder stratosphere emits less long-wave radiation

downward, thus cooling the troposphere. Overall, the cooling dominates; the

IPCC concludes that "observed stratospheric O3 losses over the past two


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decades have caused a negative forcing of the surface-troposphere system" of

about 0.15 0.10 watts per square meter (W/m).

y One of the strongest predictions of the greenhouse effect is that the stratosphere

will cool. Although this cooling has been observed, it is not trivial to separate the

effects of changes in the concentration of greenhouse gases and ozone

depletion since both will lead to cooling. However, this can be done by numerical

stratospheric modeling. Results from the National Oceanic and Atmospheric

Administration's Geophysical Fluid Dynamics Laboratory show that above 20 km

(12.4 miles), the greenhouse gases dominate the cooling.

y Ozone depleting chemicals are also greenhouse gases. The increases in

concentrations of these chemicals have produced 0.34 0.03 W/m of radiative

forcing, corresponding to about 14% of the total radiative forcing from increases

in the concentrations of well-mixed greenhouse gases.

y The long term modeling of the process, its measurement, study, design of

theories and testing take decades to both document, gain wide acceptance, and

ultimately become the dominant paradigm. Several theories about the destruction

of ozone, were hypothesized in the 1980s, published in the late 1990s, and are

currently being proven. Dr Drew Schindell, and Dr Paul Newman, NASA

Goddard, proposed a theory in the late 1990s, using a SGI Origin 2000

supercomputer, that modeled ozone destruction, accounted for 78% of the ozone

destroyed. Further refinement of that model, accounted for 89% of the ozone

destroyed, but pushed back the estimated recovery of the ozone hole from 75

years to 150 years. (An important part of that model is the lack of stratospheric

flight due to depletion of fossil fuels.)

Misconceptions about ozone depletion

CFCs are "too heavy" to reach the stratosphere

It is sometimes stated that since CFC molecules are much heavier than nitrogen or

oxygen, they cannot reach the stratosphere in significant quantities. But atmospheric


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gases are not sorted by weight; the forces of wind (turbulence) are strong enough to

fully intermix gases in the atmosphere. CFCs are heavier than air, but just like argon,

krypton and other heavy gases with a long lifetime, they are uniformly distributed

throughout the turbosphere and reach the upper atmosphere.

Man-made chlorine is insignificant compared to natural sources

Another objection occasionally voiced is that It is generally agreed that natural sources

of tropospheric chlorine (volcanoes, ocean spray, etc.) are four to five orders of

magnitude larger than man-made sources. While strictly true, tropospheric chlorine is

irrelevant; it is stratospheric chlorine that affects ozone depletion. Chlorine from ocean

spray is soluble and thus is washed out by rainfall before it reaches the stratosphere.

CFCs, in contrast, are insoluble and long-lived, which allows them to reach the

stratosphere. Even in the lower atmosphere there is more chlorine present in the form of

CFCs and related haloalkanes than there is in HCl from salt spray, and in the

stratosphere halocarbons dominate overwhelmingly. Only one of these halocarbons,

methyl chloride, has a predominantly natural source, and it is responsible for about 20

percent of the chlorine in the stratosphere; the remaining 80% comes from manmade

compounds.


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Very large volcanic eruptions can inject HCl directly into the stratosphere, but direct

measurementshave shown that their contribution is small compared to that of chlorine

from CFCs. A similar erroneous assertion is that soluble halogen compounds from the

volcanic plume of Mount Erebus on Ross Island, Antarctica are a major contributor to

the Antarctic ozone hole.

An ozone hole was first observed in 1956

G.M.B. Dobson (Exploring the Atmosphere, 2nd Edition, Oxford, 1968) mentioned that

when springtime ozone levels over Halley Bay were first measured in 1956, he was

surprised to find that they were ~320 DU, about 150 DU below spring levels, ~450 DU,

in the Arctic. These, however, were at this time the known normal climatological values

because no other antarctic ozone data were available. What Dobson describes is

essentially the baseline from which the ozone hole is measured: actual ozone hole

values are in the 150100 DU range.

The discrepancy between the Arctic and Antarctic noted by Dobson was primarily a

matter of timing: during the Arctic spring ozone levels rose smoothly, peaking in April,

whereas in the Antarctic they stayed approximately constant during early spring, rising

abruptly in November when the polar vortex broke down.

The behavior seen in the Antarctic ozone hole is distinctly different. Instead of staying

constant, early springtime ozone levels suddenly drop from their already low winter

values, by as much as 50%, and normal values are not reached again until December.

If the theory were correct, the ozone hole should be above the sources of CFCs

CFCs are well mixed in the troposphere and the stratosphere. The reason the ozone

hole occurs above Antarctica is not because there are more CFCs there but because

the low temperatures due to the polar vortex allow polar stratospheric clouds to form.

There have been anomalous discoveries of significant, serious, localized "holes" above

other parts of the globe.


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The "ozone hole" is a hole in the ozone layer

When the "ozone hole" forms, essentially all of the ozone in the lower stratosphere is

destroyed. The upper stratosphere is much less affected, however, so that the overall

amount of ozone over the continent declines by 50 percent or more. The ozone hole

does not go all the way through the layer; on the other hand, it is not a uniform 'thinning'

of the layer either. It is a "hole" in the sense of "a hole in the ground", that is, a

depression; not in the sense of "a hole in the windshield."

OZONE DEPLETION SOLUTIONS

y The discovery of the ozone depletion problem came as a great surprise. Now,

action must be taken to ensure that the ozone layer is not destroyed.

y Because CFCs are so widespread and used in such a great variety of products,

limiting their use is hard. Also, since many products already contain components

that use CFCs, it would be difficult if not impossible to eliminate those CFCs

already in existence.

y The CFC problem may be hard to solve because there are already great

quantities of CFCs in the environment. CFCs would remain in the stratosphere

for another 100 years even if none were ever produced again.y Despite the difficulties, international action has been taken to limit CFCs. In the

Montreal Protocol, 30 nations worldwide agreed to reduce usage of CFCs and

encouraged other countries to do so as well.

y However, many environmentalists felt the treaty did "too little, too late", as the

Natural Resources Defense Council put it. The treaty asked for CFC makers to

only eliminate half of their CFC production, making some people feel it was

inadequate.

y By the year 2000, the US and twelve nations in Europe have agreed to ban all

use and production of CFCs. This will be highly significant, because these

countries produce three quarters of the CFCs in the world.


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y Many other countries have signed treaties and written laws restricting the use of

CFCs. Companies are finding substitutes for CFCs, and people in general are

becoming more aware of the dangers of ozone depletion.


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CHAPTER 2

ACID RAIN

INTRODUCTION

Acid rain is rain or any other form of precipitation that is unusually acidic, i.e. elevated

levels of hydrogen ions (low pH). It has harmful effects on plants, aquatic animals, and

infrastructure. Acid rain is mostly caused by emissions of compounds of sulfur, nitrogen,

and carbon which react with the water molecules in the atmosphere to produce acids.

However, it can also be caused naturally by the splitting of nitrogen compounds by the

energy produced by lightning strikes, or the release of sulfur dioxide into the

atmosphere by phenomena of volcano eruptions.

Rain is slightly acidic because it contains dissolved carbon dioxide (CO2). Sulpher

dioxide (SO2) and Nitrogen oxides (NOx) which are normally present in the air. Acid

rain contains more acidity than the normal value because of presence of acidions due to

the dissolution of these gases present in higher concentration. Acid rain, therefore, is

the direct consequence of air pollution caused by gaseous emissions from industrial

sources, burning of fuels (thermal plants, chimneys of brick-kilns or sugar mills.) and

vehicular emissions. It is not necessary that acid rain will occur locally near the sources

of air pollution. Due to the movement of air, acid rain may occur for away from the

source. For instance, U.K. contributes 26% of the acidic sulpher deposited in the

Netherlands, 23% in Norway and 12% in Sweden. Acid emissions arise naturally from

volcanoes, forest fires and biological decomposition, especially in the oceans. But their

contribution to a acid rain are SO2, NOx and to a lesser extent CO2 and HC1 gas. SO2

pollutions is mostly contributed by thermal power plants, refineries industry and NOx

form road transport, power stations and industry. The acid gas concentrations in the air

will vary according to location, time and weather conditions.


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DEFINITION

"Acid rain" is a popular term referring to the deposition of wet (rain, snow, sleet, fog and

cloudwater, dew) and dry (acidifying particles and gases) acidic components. A more

accurate term is acid deposition.

Distilled water, which contains no carbon dioxide, has a neutral pH of 7. Liquids with a

pH less than 7 are acidic, and those with a pH greater than 7 are bases. Clean or

unpolluted rain has a slightly acidic pH of about 5.2, because carbon dioxide and water

in the air react together to form carbonic acid, a weak acid (pH 5.6 in distilled water), but

unpolluted rain also contains other chemicals.

H2O (l) + CO2 (g) H2CO3 (aq)

Carbonic acid then can ionize in water forming low concentrations of hydronium and

carbonate ions:

2 H2O (l) + H2CO3 (aq) CO32 (aq) + 2 H3O

+ (aq)

Acid deposition as an environmental issue would include additional acids to H 2CO3.


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HISTORY

Since the Industrial Revolution, emissions of sulfur dioxide and nitrogen oxides to the

atmosphere have increased. In 1852, Robert Angus Smith was the first to show the

relationship between acid rain and atmospheric pollution in Manchester, England.

Though acidic rain was discovered in 1852, it was not until the late 1960s that scientists

began widely observing and studying the phenomenon. The term "acid rain" was

generated in 1972. Canadian Harold Harvey was among the first to research a "dead"

lake. Public awareness of acid rain in the U.S increased in the 1970s after the New York

Times promulgated reports from the Hubbard Brook Experimental Forest in New

Hampshire of the myriad deleterious environmental effects demonstrated to result from

it.

Occasional pH readings in rain and fog water of well below 2.4 have been reported in

industrialized areas. Industrial acid rain is a substantial problem in Europe, China,

Russia and areas down-wind from them. These areas all burn sulfur-containing coal to

generate heat and electricity. The problem of acid rain not only has increased with

population and industrial growth, but has become more widespread. The use of tall

smokestacks to reduce local pollution has contributed to the spread of acid rain by


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releasing gases into regional atmospheric circulation. Often deposition occurs a

considerable distance downwind of the emissions, with mountainous regions tending to

receive the greatest deposition (simply because of their higher rainfall). An example of

this effect is the low pH of rain (compared to the local emissions) which falls in

Scandinavia.

EMISSIONS OF CHEMICALS LEADING TO ACIDIFICATION

The most important gas which leads to acidification is sulfur dioxide. Emissions of

nitrogen oxides which are oxidized to form nitric acid are of increasing importance due

to stricter controls on emissions of sulfur containing compounds. 70 Tg(S) per year in

the form of SO2 comes from fossil fuel combustion and industry, 2.8 Tg(S) from wildfires

and 7-8 Tg(S) per year from volcanoes.

Natural phenomena

The principal natural phenomena that contribute acid-producing gases to the

atmosphere are emissions from volcanoes and those from biological processes that

occur on the land, in wetlands, and in the oceans. The major biological source of sulfur

containing compounds is dimethyl sulfide.

Acidic deposits have been detected in glacial ice thousands of years old in remote parts

of the globe.

Human activity


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The coal-fired Gavin Power Plant in Cheshire, Ohio

The principal cause of acid rain is sulfur and nitrogen compounds from human sources,

such as electricity generation, factories, and motor vehicles. Coal power plants are one

of the most polluting. The gases can be carried hundreds of kilometres in the

atmosphere before they are converted to acids and deposited. In the past, factories had

short funnels to let out smoke, but this caused many problems locally; thus, factories

now have taller smoke funnels. However, dispersal from these taller stacks causes

pollutants to be carried farther, causing widespread ecological damage.

Chemical processes

Combustion of fuels creates sulfur dioxide and nitric oxides. They are converted into

sulfuric acid and nitric acid.

Gas phase chemistry

In the gas phase sulfur dioxide is oxidized by reaction with the hydroxyl radical via an

intermolecular reaction:

SO2 + OH HOSO2

which is followed by:

HOSO2 + O2 HO2 + SO3

In the presence of water, sulfur trioxide (SO3) is converted rapidly to sulfuric acid:

SO3 (g) + H2O (l) H2SO4 (l)

Nitrogen dioxide reacts with OH to form nitric acid:

NO2 + OH HNO3


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Chemistry in cloud droplets

When clouds are present, the loss rate of SO2 is faster than can be explained by gas

phase chemistry alone. This is due to reactions in the liquid water droplets.

Hydrolysis

Sulfur dioxide dissolves in water and then, like carbon dioxide, hydrolyses in a series of

equilibrium reactions:

SO2 (g) + H2O SO2H2O

SO2H2O H+ + HSO3

HSO3- H+ + SO3

2

Oxidation

There are a large number of aqueous reactions that oxidize sulfur from S(IV) to S(VI),

leading to the formation of sulfuric acid. The most important oxidation reactions are with

ozone, hydrogen peroxide and oxygen (reactions with oxygen are catalyzed by iron and

manganese in the cloud droplets).

Acid deposition

Processes involved in acid deposition (SO2 and NOx play a significant role in acid rain).

Wet deposition

Wet deposition of acids occurs when any form of precipitation (rain, snow, etc.) removes

acids from the atmosphere and delivers it to the Earth's surface. This can result from the

deposition of acids produced in the raindrops (see aqueous phase chemistry above) orby the precipitation removing the acids either in clouds or below clouds. Wet removal of

both gases and aerosols are both of importance for wet deposition.


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Dry deposition

Acid deposition also occurs via dry deposition in the absence of precipitation. This can

be responsible for as much as 20 to 60% of total acid deposition. This occurs when

particles and gases stick to the ground, plants or other surfaces.

ADVERSE EFFECTS

Acid deposition changes the chemistry of the environment. It affects water bodies such

as ponds and lakes, river and streams, and bays and estuaries by increasing their

acidity, in some cases to the point where aquatic animals and plants begin to die off.

The lowered pH may liberate metals bound in the minerals of the bedrock and soils

surrounding a waterbody, sometimes to a toxic effect.


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Acid deposition damages vegetation as well. Scientists have observed leaf damage

attributable to acid rain that limits the plant's ability to grow and sustain itself. Damage to

forests has also been well documented; acid deposition reacts chemically with forest

soils, leaching away nutrients vital to tree growth while at the same time mobilizing toxic

metals in the soil.

While it is less well documented, some scientists have expressed a concern that acid

deposition may adversely affect land dwelling animals as well, through the mobilization

of metals in drinking water and through the uptake of metals by plants that are later

consumed by animals. It is likely that humans would be similarly affected. It is clear that

human health is compromised in those populations chronically exposed to airborne

concentrations of sulfates and nitrates found downwind of heavily industrialized areas.

Acid deposition damages man-made structures as well; limestone, marble, and

sandstone are susceptible to damage from acid deposition, as are metals, paints,

textiles and ceramics. Repairing the damage caused by acid rain to buildings and

monuments costs millions of dollars per year.

While it is true that acid deposition is a type and consequence of air pollution, its effects

are not evenly distributed. Geography, topography, meteorology, and the chemistry of

soils and bedrock all play a role in what the effect of acid deposition will be. Alkaline or

basic soils, for example, have some ability to resist a change in their pH due to the

buffering effect of certain minerals in their makeup; less alkaline soils have less ability to

resist a change. Similarly waterbodies situated on an alkaline bedrock is more resistant

to lowering its pH that is less alkaline bedrock.

Distance from the source of the air pollution plays a role in the rate at which acid

deposition occurs, as do prevailing wind direction and elevation. It is known for example

that the eastern half of North America has been more heavily damaged by acid

deposition than has the western half; it is also true that (in general) the most severe

damage in the east has occurred to forests and waterbodies at higher elevations.

Clean Air Act


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Public concern about the environment, and about air pollution as a public health issue

led to the passage of the Clean Air Act in 1970. By the end of the 1980s the adverse

effects of acid deposition had been so well documented that in 1990 specific

amendments were added to the Clean Air Act to reduce acid deposition.

Still, there is reason to be optimistic. Studies suggest that it is possible for eco-systems

damaged by acid deposition to recover. The rate at which recovery occurs and the

extent to which the recovery happens is dependent upon the magnitude of the

reductions in sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions, and the time it

takes to achieve these emission reductions. For much of the northeastern U.S., it has

been estimated that upwards to an 80 percent reduction in utility emissions of sulfur

dioxide (SO2) (beyond those called for under Title IV) and the implementation of

controls for nitrogen oxides (NOx) will be required for eco-system recovery. Even with

these emission reductions, substantial eco-system recovery may not occur for another

25 years or more.

Critical Loads

The term 'critical load' implies a tipping point, or threshold. Most generally, the critical

load may be defined as the maximum load that a system can tolerate before failing. As

applied to environmental issues, however, critical load usually refers to exposure to

pollutants. An environmental critical load is an estimate of the level of exposure to one

or more pollutants below which no harmful effects are known to occur to specified

elements within an ecosystem.

The use of critical loads within the context of air quality management is premised on the

notion that the effectiveness air quality policy is reflected in ecosystem impacts. The

critical load concept is uniquely well suited toward informing air quality policy because

its receptor-based approach takes into account both the spatial and topographical

variables of atmospheric deposition. As it applies to the atmospheric deposition of acid

forming compounds then, a critical load is that level of exposure to sulfur and nitrogen

compounds below which no harmful effects are known to occur within a specified


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environment (or ecosystem). The approach used to identify critical loads for sulfur and

nitrogen in Maine's forest ecosystem is an ecological assessment based on an overall

(steady-state) ecosystem budget for nutrient cations of calcium (Ca 2+ ), magnesium

(Mg 2+ ), and potassium (K + ). This budget exists within a dynamic system of nutrient

inputs, exports, and recycling.

In its simplest terms, the inputs to the nutrient budget for the Maine forest ecosystem

include the addition of the nutrients Ca, Mg, and K through atmospheric deposition; acid

forming compounds of sulfur (S) and nitrogen (N) are also introduced through

deposition. Additional inputs of Ca, Mg, and K result from the chemical weathering of

the bedrock and soils.

The overall ecosystem budget is based upon the relative values of the inputs to and

exports from the system. A condition where nutrient inputs exceed exports suggests

that a sufficient state of biologic capacity exists for an ecosystem. Conversely, a

condition where nutrient exports exceed inputs suggests a net nutrient deficit and

increasing soil acidification; conditions ultimately unsustainable for a ecosystem over

the long term. Many studies have demonstrated that inadequate nutrient levels lead to

poor forest health and reduced growth rates.


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This chart shows that not all fish, shellfish, or the insects that they eat can tolerate the

same amount of acid; for example, frogs can tolerate water that is more acidic (i.e., has

a lower pH) than trout.

Acid rain has been shown to have adverse impacts on forests, freshwaters and soils,

killing insect and aquatic life-forms as well as causing damage to buildings and having

impacts on human health.

EFFECTS OF ACID RAIN


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The most important effects are: damage to freshwater aquatic life, damage of

vegetation and damage to buildings and material.

Damage to aquatic life

The main impact of fresh water acidification is a reduction in diversity and populations of

fresh water species. The effect on soil and rock will depend upon the in situ capacity

called buffering capacity to neutralize the acids. The soil organisms are killed in acid

rain where soils have limited buffering capacity. The acidic leaf litter in forest areas adds

to the nutrient leaching effects of acid rain. This scavenging from cloud increases the

amount of pollution deposited. Trees are quite effective in intercepting the air borne

pollutants than other types of upland vegetation. In the areas of high acid deposition

and poor buffering in the lakes, a PH less than 5 has become common. At PH 5, fish life

and frogs begin to disappear. By PH 4, 5, virtually all aquatic life has gone. Acid rain

releases metals particularly aluminium-from the soil, which can build up in lake water to

levels that are toxic to fish and other organisms. A decline in fish and amphibian

population will affect the food chain of birds and mammals that depend on them for

food.

Surface waters and aquatic animals

Both the lower pH and higher aluminum concentrations in surface water that occur as a

result of acid rain can cause damage to fish and other aquatic animals. At pHs lower

than 5 most fish eggs will not hatch and lower pHs can kill adult fish. As lakes and rivers

become more acidic biodiversity is reduced. Acid rain has eliminated insect life and

some fish species, including the brook trout in some lakes, streams, and creeks in

geographically sensitive areas, such as the Adirondack Mountains of the United States.

However, the extent to which acid rain contributes directly or indirectly via runoff from

the catchment to lake and river acidity (i.e., depending on characteristics of the

surrounding watershed) is variable. The United States Environmental Protection

Agency's (EPA) website states: "Of the lakes and streams surveyed, acid rain caused

acidity in 75 percent of the acidic lakes and about 50 percent of the acidic streams".


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Damage to Trees and Plants

For some years there has been concern about the apparent deterioration of trees and

other vegetation. It is not easy to establish the cause of damage: pollution, drought,

frost, pests and forst management methods can all affect tree health. SO2 has a directtoxic effect on trees and in parts of central Europe for example where SO2 levels are

very high, extensive areas of forest have been damaged or destroyed. Acid deposition

may combine with other factors to affect tree health; for instance by making trees more

susceptible to attack by pests, or by acidifying soils which may cause loss of essential

nutrients such as magnesium, thus impairing tree growth. Nitrogen and sulphur are both

plant nutrients and deposition can upset the balance of natural plant communities by

encouraging the growth of other plant species. Secondary pollutants like ozone are also

known to exacerbate the effects of acid deposition.

Forests and other vegetation

Adverse effects may be indirectly related to acid rain, like the acid's effects on soil or

high concentration of gaseous precursors to acid rain. High altitude forests are

especially vulnerable as they are often surrounded by clouds and fog which are more

acidic than rain.

Other plants can also be damaged by acid rain, but the effect on food crops is

minimized by the application of lime and fertilizers to replace lost nutrients. In cultivated

areas, limestone may also be added to increase the ability of the soil to keep the pH

stable, but this tactic is largely unusable in the case of wilderness lands. When calcium

is leached from the needles of red spruce, these trees become less cold tolerant and

exhibit winter injury and even death.

Damage to Buildings and Materials

All historic buildings suffer damage and decay with time. Natural weathering causes

some of this but there is no doubt that air pollution, particularly SO2, also plays an

important part. SO2 penetrated porous stones such as limestone and is converted to


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calcium sulphate, which causes gradual crumbling. Most building damage happens in

urban areas where there are many SO2 emitters (domestic chimneys, factories and

heating plant). The introduction of the Clean Air Acts and the replacement of coal fires

by gas and electricity has greatly reduced sulphur dioxide levels in urban areas. Other

materials badly affected by pollutant gases include marble, stained glass, most metals

and paint. Poorly set or fractured concrete may also allow sulphates to penetrate and

corrode the steel reinforcement inside.

Soils

Soil biology and chemistry can be seriously damaged by acid rain. Some microbes are

unable to tolerate changes to low pHs and are killed. The enzymes of these microbes

are denatured (changed in shape so they no longer function) by the acid. The

hydronium ions of acid rain also mobilize toxins such as aluminium, and leach away

essential nutrients and minerals such as magnesium.

2 H+ (aq) + Mg2+ (clay) 2 H+ (clay) + Mg2+ (aq)

Soil chemistry can be dramatically changed when base cations, such as calcium and

magnesium, are leached by acid rain thereby affecting sensitive species, such as sugar

maple (Acer saccharum).

Human health

Scientists have suggested direct links to human health. Fine particles, a large fraction of

which are formed from the same gases as acid rain (sulfur dioxide and nitrogen

dioxide), have been shown to cause illness and premature deaths such as cancer and

other diseases.


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Other adverse effects

Effect of acid rain on statues and memorable buildings like Taj-Mahal in India

Acid rain can also cause damage to certain building materials and historical

monuments. This results when the sulfuric acid in the rain chemically reacts with thecalcium compounds in the stones (limestone, sandstone, marble and granite) to create

gypsum, which then flakes off.

CaCO3 (s) + H2SO4 (aq) CaSO4 (aq) + CO2 (g) + H2O (l)

This result is also commonly seen on old gravestones where the acid rain can cause the

inscription to become completely illegible. Acid rain also causes an increased rate of

oxidation for metals, and in particular copper and bronze. Visibility is also reduced bysulfate and nitrate aerosols and particles in the atmosphere.

AFFECTED AREAS

Particularly badly affected places around the globe include most of Europe (particularly

Scandinavia with many lakes with acidic water containing no life and many trees dead)

many parts of the United States (states like New York are very badly affected) and

South Western Canada. Other affected areas include the South Eastern coast of Chinaand Taiwan.


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POTENTIAL PROBLEM AREAS IN THE FUTURE

Places like much of South Asia (Indonesia, Malaysia and Thailand), Western South

Africa (the country), Southern India and Sri Lanka and even West Africa (countries like

Ghana, Togo and Nigeria) could all be prone to acidic rainfall in the future.

REDUCING ACID POLLUTION

Technical solutions

In the United States, many coal-burning power plants use Flue gas desulfurization

(FGD) to remove sulfur-containing gases from their stack gases. An example of FGD is

the wet scrubber which is commonly used in the U.S. and many other countries. A wet

scrubber is basically a reaction tower equipped with a fan that extracts hot smoke stack

gases from a power plant into the tower. Lime or limestone in slurry form is also injected

into the tower to mix with the stack gases and combine with the sulfur dioxide present.

The calcium carbonate of the limestone produces pH-neutral calcium sulfate that is

physically removed from the scrubber. That is, the scrubber turns sulfur pollution into

industrial sulfates.

In some areas the sulfates are sold to chemical companies as gypsum when the purityof calcium sulfate is high. In others, they are placed in landfill. However, the effects of

acid rain can last for generations, as the effects of pH level change can stimulate the

continued leaching of undesirable chemicals into otherwise pristine water sources,

killing off vulnerable insect and fish species and blocking efforts to restore native life.

Automobile emissions control reduces emissions of nitrogen oxides from motor

vehicles.

Sulphur Dioxide


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The sulphur which is present in nearly all fossil fuels combines with oxygen when the

fuel is burnt and is released into the atmosphere as SO2 gas. These emissions can be

reduced by measures taken before, during, or after the combustion process.

One approach is to use fuels which naturally have little sulphur in them. The sulphurcontent of coal can vary considerably. Some fuels may be treated to reduce their

sulphur content, but effective treatment is expensive. Demand for low sulphur fuels is

increasing as more countries develop programmes to reduce sulphur pollution, so they

are becoming more expensive. During combustion it is possible to reduce the eventual

emissions of SO2 by the introduction of a sorbent such as limestone. The potential for

sulphur reduction by this approach depends on the type of furnace or boiler. After

combustion, sulphur can be removed from flue gases or scrubbed. This process is

known as the flue gas desulphurization (FGD). In most FGD system a mixture of

limestone and water is sprayed into the flue gas. The SO2 is converted to gypsum

(calcium sulphate), which can be used in the manufacture of plaster products. However,

FGD systems of this type are expensive and use considerable amounts of limestone. If

all power stations were fitted with FGD, gypsum production would exceed requirements,

leading to a waste disposal problem. Although such a programme would increase

limestone extraction by about 5%, there would be a useful reduction in gypsum

quarrying. An alternative to limestone FGD systems is the regenerative FGD approach

in which SO2 is captured by a substance which can be recycled. Sulphur or sulphuric

acid is obtained as a by-product and can be used in the chemical industry. Again, there

are limits to the amount of by-product which industry can use.

Although FGD can reduce sulphur emissions by up to 90%, such systems use extra

energy and, therefore, increase emissions of the greenhouse gas CO2.

Nitrogen Oxides

NOx is produced partly from the oxidation of nitrogen contained in the fuel and partly as

a result of high temperature and pressure combustion, which oxidizes nitrogen in the

air. Furnace burners can be changed to reduce outputs of NOx by up to 40% (low-NOx


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burners). NOx in flue gas can be reduced by adding ammonia and passing it over a

catalyst to produce nitrogen and water. This process is called selective catalytic

reduction (SCR) and can reduce NOx from combustion plant by 85%, NOx produced by

cars can also be treated by using catalysts; fitting a catalytic converter to the exhaust

system reduces NOx emissions by up to 90%, although it may increase emissions of

CO2.

Other Options

Since most acid pollution comes from burning fossil fuels, one way of reducing

emissions is to reduce the overall demand for energy by encouraging energy

conservation and improving the efficiency of electricity generation. Another option is to

develop non-fossil fuel energy sources such as nuclear power or renewable energy

(solar, wind, tidal power, etc.) However these have their own environmental problems

which must be balanced against those of fossil fuels.

International treaties

A number of international treaties on the long range transport of atmospheric pollutants

have been agreed e.g. Sulphur Emissions Reduction Protocol under the Convention on

Long-Range Transboundary Air Pollution.

Emissions trading

In this regulatory scheme, every current polluting facility is given or may purchase on an

open market an emissions allowance for each unit of a designated pollutant it emits.

Operators can then install pollution control equipment, and sell portions of their

emissions allowances they no longer need for their own operations, thereby recovering

some of the capital cost of their investment in such equipment. The intention is to giveoperators economic incentives to install pollution controls.

The first emissions trading market was established in the United States by enactment of

the Clean Air Act Amendments of 1990. The overall goal of the Acid Rain Program


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CHAPTER 3

CLIMATE CHANGE

INTRODUCTION

Climate change is a change in the statistical distribution of weather over periods of

time that range from decades to millions of years. It can be a change in the average

weather or a change in the distribution of weather events around an average (for

example, greater or fewer extreme weather events). Climate change may be limited to a

specific region, or may occur across the whole Earth.

In recent usage, especially in the context of environmental policy, climate changeusually refers to changes in modern climate. It may be qualified as anthropogenic

climate change, more generally known as global warming.

For information on temperature measurements over various periods, and the data

sources available, see temperature record. For attribution of climate change over the

past century, see attribution of recent climate change.

Causes

Factors that can shape climate are climate forcings. These include such processes as

variations in solar radiation, deviations in the Earth's orbit, mountain-building and

continental drift, and changes in greenhouse gas concentrations. There are a variety of

climate change feedbacks that can either amplify or diminish the initial forcing. Some

parts of the climate system, such as the oceans and ice caps, respond slowly in

reaction to climate forcing because of their large mass. Therefore, the climate system

can take centuries or longer to fully respond to new external forcings.


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Plate tectonics

Over the course of millions of years, the motion of tectonic plates reconfigures global

land and ocean areas and generates topography. This can affect both global and local

patterns of climate and atmosphere-ocean circulation.[1]

The position of the continents determines the geometry of the oceans and therefore

influences patterns of ocean circulation. The locations of the seas are important in

controlling the transfer of heat and moisture across the globe, and therefore, in

determining global climate. A recent example of tectonic control on ocean circulation is

the formation of the Isthmus of Panama about 5 million years ago, which shut off direct

mixing between the Atlantic and Pacific Oceans. This strongly affected the ocean

dynamics of what is now the Gulf Stream and may have led to Northern Hemisphere ice

cover. Earlier, during the Carboniferous period, plate tectonics may have triggered the

large-scale storage of carbon and increased glaciation. Geologic evidence points to a

"megamonsoonal" circulation pattern during the time of the supercontinent Pangaea,

and climate modeling suggests that the existence of the supercontinent was conducive

to the establishment of monsoons.

More locally, topography can influence climate. The existence of mountains (as aproduct of plate tectonics through mountain-building) can cause orographic

precipitation. Humidity generally decreases and diurnal temperature swings generally

increase with increasing elevation. Mean temperature and the length of the growing

season also decrease with increasing elevation. This, along with orographic

precipitation, is important for the existence of low-latitude alpine glaciers and the varied

flora and fauna along at different elevations in montane ecosystems.

The size of continents is also important. Because of the stabilizing effect of the oceans

on temperature, yearly temperature variations are generally lower in coastal areas than

they are inland. A larger supercontinent will therefore have more area in which climate

is strongly seasonal than will several smaller continents and/or island arcs.


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Solar output

F:\world\Climate change - Wikipedia, the free encyclopedia_files\180px-Solar_Activity_Proxies.png

Variations in solar activity during the last several centuries based on observations of

sunspots and beryllium isotopes.

The sun is the predominant source for energy input to the Earth. Both long- and short-

term variations in solar intensity are known to affect global climate.

Early in Earth's history the sun emitted only 70% as much power as it does today. With

the same atmospheric composition as exists today, liquid water should not have existed

on Earth. However, there is evidence for the presence of water on the early Earth, in the

Hadean and Archean eons, leading to what is known as the faint young sun paradox.

Hypothesized solutions to this paradox include a vastly different atmosphere, with much

higher concentrations of greenhouse gases than currently exist Over the following

approximately 4 billion years, the energy output of the sun increased and atmospheric

composition changed, with the oxygenation of the atmosphere being the most notable

alteration. The luminosity of the sun will continue to increase as it follows the main

sequence. These changes in luminosity, and the sun's ultimate death as it becomes a

red giant and then a white dwarf, will have large effects on climate, with the red giant

phase possibly ending life on Earth.

Solar output also varies on shorter time scales, including the 11-year solar cycle andlonger-term modulations. The 11-year sunspot cycle produces low-latitude warming and

high-latitude cooling over limited areas of statistical significance in the stratosphere with

an amplitude of approximately 1.5C. But although "variability associated with the 11-yr

solar cycle has a significant influence on stratospheric temperatures. ...there is still no


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consensus on the exact magnitude and spatial structure". These stratospheric variations

are consistent with the idea that excess equatorial heating can drive thermal winds. In

the near-surface troposphere, there is only a small change in temperature (on the order

of a tenth of a degree, and only statistically significant in limited areas underneath the

peaks in stratospheric zonal wind speed) due to the 11-year solar cycle. Solar intensity

variations are considered to have been influential in triggering the Little Ice Age, and for

some of the warming observed from 1900 to 1950. The cyclical nature of the sun's

energy output is not yet fully understood; it differs from the very slow change that is

happening within the sun as it ages and evolves, with some studies pointing toward

solar radiation increases from cyclical sunspot activity affecting global warming

Orbital variations

Slight variations in Earth's orbit lead to changes in the seasonal distribution of sunlight

reaching the Earth's surface and how it is distributed across the globe. There is very

little change to the area-averaged annually-averaged sunshine; but there can be strong

changes in the geographical and seasonal distrubution. The three types of orbital

variations are variations in Earth's eccentricity, changes in the tilt angle of Earth's axis of

rotation, and precession of Earth's axis. Combined together, these produce Milankovitch

cycles which have a large impact on climate and are notable for their correlation to

glacial and interglacial periods, their correlation with the advance and retreat of the

Sahara and for their appearance in the stratigraphic record.

Volcanism

Volcanism is a process of conveying material from the crust and mantle of the Earth to

its surface. Volcanic eruptions, geysers, and hot springs, are examples of volcanic

processes which release gases and/or particulates into the atmosphere.

Eruptions large enough to affect climate occur on average several times per century,

and cause cooling (by partially blocking the transmission of solar radiation to the Earth's

surface) for a period of a few years. The eruption of Mount Pinatubo in 1991, the


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second largest terrestrial eruption of the 20th century (after the 1912 eruption of

Novarupta) affected the climate substantially. Global temperatures decreased by about

0.5 C (0.9 F). The eruption of Mount Tambora in 1815 caused the Year Without a

Summer. Much larger eruptions, known as large igneous provinces, occur only a few

times every hundred million years, but may cause global warming and mass extinctions.

Volcanoes are also part of the extended carbon cycle. Over very long (geological) time

periods, they release carbon dioxide from the Earth's crust and mantle, counteracting

the uptake by sedimentary rocks and other geological carbon dioxide sinks. According

to the US Geological Survey, however, estimates are that human activities generate

more than 130 times the amount of carbon dioxide emitted by volcanoes.

Ocean variability

F:\world\Climate change - Wikipedia, the free encyclopedia_files\180px-Ocean_circulation_conveyor_belt.jpg

A schematic of modern thermohaline circulation

The ocean is a fundamental part of the climate system. Short-term fluctuations (years to

a few decades) such as the El NioSouthern Oscillation, the Pacific decadal

oscillation, the North Atlantic oscillation, and the Arctic oscillation, represent climate

variability rather than climate change. On longer time scales, alterations to ocean

processes such as thermohaline circulation play a key role in redistributing heat by

carrying out a very slow and extremely deep movement of water, and the long-termredistribution of heat in the world's oceans.


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Human influences

Anthropogenic factors are human activities that change the environment. In some cases

the chain of causality of human influence on the climate is direct and unambiguous (for

example, the effects of irrigation on local humidity), whilst in other instances it is less

clear. Various hypotheses for human-induced climate change have been argued for

many years. Presently the scientific consensus on climate change is that human activity

is very likely the cause for the rapid increase in global average temperatures over the

past several decades.[24] Consequently, the debate has largely shifted onto ways to

reduce further human impact and to find ways to adapt to change that has already

occurred.

Of most concern in these anthropogenic factors is the increase in CO2 levels due to

emissions from fossil fuel combustion, followed by aerosols (particulate matter in the

atmosphere) and cement manufacture. Other factors, including land use, ozone

depletion, animal agriculture and deforestation, are also of concern in the roles they

play - both separately and in conjunction with other factors - in affecting climate,

microclimate, and measures of climate variables.

Physical evidence for climatic change

Evidence for climatic change is taken from a variety of sources that can be used to

reconstruct past climates. Reasonably complete global records of surface temperature

are available beginning from the mid-late 1800s. For earlier periods, most of the

evidence is indirect climatic changes are inferred from changes in proxies, indicators

that reflect climate, such as vegetation, ice cores, dendrochronology, sea level change,

and glacial geology.

Historical & Archaeological evidence

Climate change in the recent past may be detected by corresponding changes in

settlement and agricultural patterns. Archaeological evidence, oral history and historical


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documents can offer insights into past changes in the climate. Climate change effects

have been linked to the collapse of various civilisations.

Glaciers

Glaciers are among the most sensitive indicators of climate change, advancing when

climate cools (for example, during the period known as the Little Ice Age) and retreating

when climate warms. Glaciers grow and shrink, both contributing to natural variability

and amplifying externally forced changes. A world glacier inventory has been compiled

since the 1970s. Initially based mainly on aerial photographs and maps, this compilation

has resulted in a detailed inventory of more than 100,000 glaciers covering a total area

of approximately 240,000 km2 and, in preliminary estimates, for the recording of the

remaining ice cover estimated to be around 445,000 km2. The World Glacier Monitoring

Service collects data annually on glacier retreat and glacier mass balance From this

data, glaciers worldwide have been found to be shrinking significantly, with strong

glacier retreats in the 1940s, stable or growing conditions during the 1920s and 1970s,

and again retreating from the mid 1980s to present.[31] Mass balance data indicate 17

consecutive years of negative glacier mass balance.

Glaciers leave behind moraines that contain a wealth of material - including organicmatter that may be accurately dated - recording the periods in which a glacier advanced

and retreated. Similarly, by tephrochronological techniques, the lack of glacier cover can

be identified by the presence of soil or volcanic tephra horizons whose date of deposit

may also be precisely ascertained.

Vegetation

A change in the type, distribution and coverage of vegetation may occur given a change

in the climate; this much is obvious. In any given scenario, a mild change in climate may

result in increased precipitation and warmth, resulting in improved plant growth and the

subsequent sequestration of airborne CO2. Larger, faster or more radical changes,


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however, may well] result in vegetation stress, rapid plant loss and desertification in

certain circumstances

Ice cores

Analysis of ice in a core drilled from a ice sheet such as the Antarctic ice sheet, can be

used to show a link between temperature and global sea level variations. The air

trapped in bubbles in the ice can also reveal the CO2 variations of the atmosphere from

the distant past,

global environmental issues- anuja joshi

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