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ON

OZONE EPLETION


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INTRODUCTION

Ozone is a natural gas composed of three atoms of oxygen. It chemical symbol is O3. It is blue

in color and has a strong odor. Normal oxygen (O2), which we breathe, has two oxygen atoms

and is colorless and odorless. Environmental scientists have classified O3into two: Good Ozone

and Bad Ozone.

Good Ozone

Good ozone(also call ed Stratospheric Ozone)occurs naturally in the upper Stratosphere. The

stratosphere is the layer of space 6 to 30 miles above the earth's surface.

Where does good Ozone come fr om?

The air is full of gases reacting with each other, even though our eyes do not see. When UV light

strikes (Oxygen) O2 molecules, they are split into two individual O atomsO and O. When

one of the O atoms combine with O2 molecule, ozone (O3) is created.


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Even though Ozone is only a small part of the gases in this layer, it plays a vital role because it

shields us from the sun's harmful UV rays. It is called Good Ozone, for obvious reasons

because it protects humans, life and animals on earth.

Bad Ozone

Bad Ozone is also known asTropospheri c Ozone,or ground level ozone. This gas is found in

the troposphere, the layer that forms the immediate atmosphere. Bad Ozone does not exist

naturally. Human actions cause chemical reactions between oxides of nitrogen (NOx) and

volatile organic compounds (VOC).

Where does bad ozone come from?

Each time there is a reaction of chemicals such as those found in cars, power plants and factoryemissions, in the presence of sunlight (UV light), Bad Ozone is created.

Bad ozone contaminates (dirties) the air and contributes to what we typically experience as

"smog" or haze.

Note that this kind of smog is different from the deadlyLondon winter type that killed 4000

people. Smog from bad ozone is usually in the summer, caused by the action of sunlight on a

mixture of hydrocarbons and oxides of nitrogen. It is known asPhotochemicalor Summer Smog.
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The Ozone Layer

This is simply a layer in the stratosphere containing a relatively high concentration of ozone.

The earth's atmosphere is divided into several layers, and each layer plays an important role. Thefirst region extending about 10km upwards from the earth's surface is called the troposphere.

Many human activities like mountain climbing, gas balloons and smaller aircrafts operate within

this region.

The next layer, extending about 15-60 km is called the stratosphere. The ozone layer is mainly

found in the lower portion of the stratosphere from approximately 20 to 30 kilometres (12 to 19

mi) above earth, though the thickness varies seasonally and geographically.

The ozone layer protects the earth from the suns UV Rays. If the ozone layer is depleted by

human action, the effects on the planet could be catastrophic.


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What is Ozone Depletion?

Ozone layer depletion, is simply the wearing out (reduction) of the amount of ozone in the

stratosphere. Unlike pollution, which has many types and causes, Ozone depletion has been

pinned down to one major human activity.

Industries that manufacture things like insulating foams, solvents, soaps, cooling things like Air

Conditioners, Refrigerators and Take-Away containers use something called

chlorofluorocarbons (CFCs). These substances are heavier than air, but over time, (2-5years)

they are carried high into the stratosphere by wind action.

Depletion begins when CFCs get into the stratosphere. Ultra violet radiation from the sun breaks

up these CFCs. The breaking up action releases Chlorine atoms. Chlorine atoms react with

Ozone, starting a chemical cycle that destroys the good ozone in that area. One chlorine atom can

break apart more than 100,000 ozone molecules.

Ozone depletiondescribes two distinct, but related observations: a slow, steady decline of about

4% per decade in the total volume ofozone inEarth'sstratosphere (theozone layer)since the late

1970s,and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions
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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 alsotropospheric ozone

depletion events,which occur near the surface in polar regions during spring.

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 iscatalytic destruction of ozone

by atomic chlorine and bromin. The main source of thesehalogen atoms in the stratosphere is

photodissociation ofchlorofluorocarbon (CFC) compounds, commonly calledfreons,and of

bromofluorocarbon compounds known ashalons.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 harmfulUVB wavelengths (280315 nm) ofultraviolet light (UV light) from passing through theEarth's

atmosphere,observed and projected decreases in ozone have generated worldwide concern

leading to adoption of theMontreal Protocol that bans the production of CFCs and halons as well

as related ozone depleting chemicals such ascarbon tetrachloride andtrichloroethane.It is

suspected that a variety of biological consequences such as increases inskin cancer,

cataracts,damage to plants, and reduction ofplanktonpopulations in the ocean'sphotic zone may

result from the increased UV exposure due to ozone depletion. The ozone layer is a layer in earth

atmosphere which contains relatively high concentration of ozone(O3) this layer observes 97-

99% of the suns high frequency ultra violet light, which is damaging to life on earth it is mainly

located in lower position of the stratsophere from approximately 13-40kms (8.1-25 mi) above

earth though the thickness varies seasonally and geographically the ozone layer was discovered

in 1913 by the physicist Charles Fabry and Heny buission.
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Ozone cycle overview

The ozone cycle

Three forms (orallotropes)of oxygen are involved in theozone-oxygen cycle:oxygen atoms (O

or atomic oxygen), oxygen gas (O2or diatomic oxygen), and ozone gas (O3or triatomic oxygen).

Ozone is formed in the stratosphere when oxygen moleculesphotodissociate after absorbing an

ultravioletphoton whose wavelength is shorter than 240 nm. This produces two oxygen atoms.

The atomic oxygen then combines with O2to create O3. Ozone molecules absorb UV light

between 310 and 200 nm, following which ozone splits into a molecule of O2and an oxygen

atom. The oxygen atom then joins up with an oxygen molecule to regenerate ozone. This is acontinuing process which terminates when an oxygen atom "recombines" with an ozone

molecule to make two O2molecules: O + O3 2 O2

Global monthly average total ozone amount.
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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 offree radical catalysts, the most important of which are

thehydroxyl radical (OH), thenitric oxide radical (NO), atomicchlorine (Cl) andbromine

(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, especiallychlorofluorocarbons (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' isPlanck's constant,'' isfrequency ofelectromagnetic radiation)

CFCl3+ h CFCl2+ Cl

The Cl and Br atoms can then destroy ozone molecules through a variety ofcatalytic cycles. In

the simplest example of such a cycle, chlorine atom reacts with an ozone 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-phasereactions 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 two years (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 ashydrogen chloride (HCl) andchlorine nitrate

(ClONO2). On a per atom basis, bromine is even more efficient than chlorine at destroying
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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 boundHF,

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.

How do volcanoes affect stratospheric ozone?

When volcanoes erupt, they produce massive clouds of ashes into the troposphere, and then they

drift upward into the stratosphere(the upper atmosphere layer where ozone gas protects humans

from UV radiation).These ashes contain high concentration of bromineand chlorine. Ashes can

stay in the stratosphere for about two to five years, and within this period, there are chemical

reactions that destroy the stratospheric ozone molecules.
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In these volcanic ashes are some chemicals including bromine and chlorine belong to a group of

highly reactive elements called halogens, that need electrons to become stable. They get these

electrons from the Ozone gas.

Ozone destroying gases like hydrogen chloride, can also be found in volcanic ashes, but they

dissolve readily in water. In many cases rain can wash down these chemicals before they get

high up into the stratosphere, but some do escape into it.

Human activities like pollution and emissions already send lots of halogen gases into the

stratospherebut, scientists have noted that halogens from volcanoes contain twice and thrice

as much halogens that human activities even produce. This means the potential of depleting the

ozone layer is higher with volcanic 'smoke'

Remember that the stratosphere is high up and that means when volcanic ash gets there, the

impact can be over a very large area, even to the size of the entire North American region.

I t is beli eved that the eruption of Mount Pinatubo (Phi li ppines) in 1991 sent th ick plumes

34km up in to the stratosphere, where it had a signi f icant impact on the ozone levels at the

time. Other l arge eruptions include Tambora, Krakatau and Agung, all of whi ch ad impacts

on ozone levels.

All in all it is known that volcanoes contribute about 18%-20% of Chlorine entering the

atmosphere, and human activities also contribute about 80%-82%.

How Ozone Depletion Affects UV Levels?

Depletion of the ozone layer has consequences on humans, animals and plants. This typicallyresults from higher UV levels reaching us on earth.

Humans

Research confirms that high levels of UV Rays cause non-melanoma skin cancer. Additionally, it

plays a major role in malignant melanoma development. UV is also linked to cataracts (a disease


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of the eye which clouds the eyes lens).

This is why it is important to wear UV protection sun-glasses and sun-cream when you stay in

the sun to minimise the UV effect on your skin and eyes.

Plants

The damage that extreme UV levels has on plants is one that our eyes do not see much, but

humans can feel the impact. Plant growth, as well as its physiological and developmental

processes are all affected negatively. These include the way plants form, timing of development

and growth, distribution of plant nutrients and metabolism, etc. These changes can have

important implications for plant competitive balance, animals that feed on these plants, plant

diseases, and biogeochemical cycles.

Marine (or water) Ecosystems

Phytoplankton form the foundation of aquatic food webs. These usually grow closer to the

surface of water, where there is enough sunlight. Changes in UV levels is known to affect the

development and growth of phytoplankton, and naturally, the fish that feed on them. UV

radiation is also know to have affect the development stages of of fish, shrimp, crab, amphibians

and other animals. When this happens, animals in the upper food chain that feed on these tiny

fishes are all affected.

Effects on Biogeochemical Cycles

The power of higher UL levels affect the natural balance of gasses (and greenhouse gases) in the

biosphere: e.g., carbon dioxide (CO2), carbon monoxide (CO), carbonyl sulfide (COS) and

ozone. Changes in UV levels can cause biosphere-atmosphere feedback resulting from the

atmospheric buildup of these gases.


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Observations on ozone layer depletion

The most pronounced decrease in ozone has been in the lowerstratosphere.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 inDobson units,abbreviated as "DU". Marked

decreases in column ozone in theAntarctic spring and early summer compared to the early 1970s

and before have been observed using instruments such as theTotal Ozone Mapping

Spectrometer (TOMS).

Lowest value of ozone measured byTOMS 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 theArctic 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 depletionSCs form more readily in the extreme cold of Antarctic stratosphere.

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 ingreenhouse gases such asCO2;however the ozone-induced cooling

appears to be dominant.

Predictions of ozone levels remain difficult. TheWorld Meteorological Organization Global

Ozone Research and Monitoring ProjectReport No. 44 comes out strongly in favor for the

Montreal Protocol, but notes that aUNEP 1994 Assessment overestimated ozone loss for the

19941997 period.

Chemicals in the atmosphere

CFCs in the atmosphere

Chlorofluorocarbons (CFCs)were invented byThomas Midgley, Jr. in the 1920s. They were

used inair conditioning/cooling units, asaerosol spray propellantsprior 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

compoundstheir 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 acatalyst,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

CFCphotolysisproducts into contact with ozone. There has been increase in the depletion also

seen due to the emissions of the cfc gases from the electrical appliances like ac, refrigerator that

are one of the essentials that we use in daily purpose.

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). Source: NASA
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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 thispolar 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 ofpolar stratospheric clouds (PSCs).

These polar stratospheric clouds(PSC) 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 thepolar vortex traps and chills air. Temperatures hover around

or below -80 C. These low temperatures form cloud particles. There are three types of PSC

clouds; nitric acid trihydrate clouds, slowly cooling water-ice clouds, and rapid cooling water-

ice(nacerous) clouds; that provide surfaces for chemical reactions that lead to ozone destruction.

Thephotochemicalprocesses involved are complex but well understood. The key observation isthat, 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 NO2from 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, however, the sun comes

out, providing energy to drive photochemical reactions, and melt the polar stratospheric clouds,

releasing the trapped compounds. Warming temperatures near the end of spring break up the
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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.

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.

Interest in ozone layer depletion

While the effect of the Antarctic ozone hole in decreasing the global ozone is relatively small,

estimated at about 4% per decade, the hole has generated a great deal of interest because:

The decrease in the ozone layer was predicted in the early 1980s to be roughly 7% over a

60 year period.

The sudden recognition in 1985 that there was a substantial "hole" was widely reported in

the press. The especially rapid ozone depletion in Antarctica had previously been

dismissed as a measurement error.

Many were worried that ozone holes might start to appear over other areas of the globe

but to date the only other large-scale depletion is a smaller ozone "dimple" observed

during the Arctic spring over the North Pole. Ozone at middle latitudes has declined, but

by a much smaller extent (about 45% decrease).

If the conditions became more severe (cooler stratospheric temperatures, more

stratospheric clouds, more active chlorine), then global ozone may decrease at a much

greater pace. Standardglobal warming theory predicts that the stratosphere will cool[

When the Antarctic ozone hole breaks up, the ozone-depleted air drifts out into nearby

areas. Decreases in the ozone level of up to 10% have been reported in New Zealand in

the month following the break-up of the Antarctic ozone hole.
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Consequences of ozone layer depletion

Since the ozone layer absorbsUVB 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 becauseUVA,

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

layerdecreases 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 surfaceUVB due to the ozone hole can be partially inferred byradiative transfer

model calculations, but cannot be calculated from direct measurements 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 thetroposphere), 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.
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Biological effects

The main public concern regarding the ozone hole has been the effects 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 ofAustralia,New

Zealand,Chile,Argentina,andSouth Africa,environmentalists have been concerned that the

increase in surface UV could be significant.

Effects on Human and Animal Health

Increased penetration of solar UV-B radiation is likely to have profound impact on human health

with potential risks of eye diseases, skin cancer and infectious diseases. UV radiation is known

to damage the cornea and lens of the eye. Chronic exposure to UV-B could lead to cataract of the

cortical and posterior subcapsular forms. UV-B radiation can adversely affect the immune

system causing a number of infectious diseases. In light skinned human populations, it is likely

to develop nonmelanoma skin cancer (NMSC). Experiments on animals show that UV exposure

decreases the immune response to skin cancers, infectious agents and other antigens

Effects on Terrestrial Plants

It is a known fact that the physiological and developmental processes of plants are affected by

UV-B radiation. Scientists believe that an increase in UV-B levels would necessitate using more

UV-B tolerant cultivar and breeding new tolerant ones in agriculture. In forests and grasslands

increased UV-B radiation is likely to result in changes in species composition (mutation) thus

altering the bio-diversity in different ecosystems. UV-B could also affect the plant community

indirectly resulting in changes in plant form, secondary metabolism, etc. These changes can have

important implications for plant competitive balance, plant pathogens and bio-geochemical

cycles.

Effects on Aquatic Ecosystems
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While more than 30 percent of the worlds animal protein for human consumption comes from

the sea alone, it is feared that increased levels of UV exposure can have adverse impacts on the

productivity of aquatic systems. High levels of exposure in tropics and subtropics may affect the

distribution of phytoplanktons which form the foundation of aquatic food webs. Reportedly a

recent study has indicated 6-12 percent reduction in phytoplankton production in the marginal

ice zone due to increases in UV-B. UV-B can also cause damage to early development stages of

fish, shrimp, crab, amphibians and other animals, the most severe effects being decreased

reproductive capacity and impaired larval development.

Effects on Bio-geo-chemical Cycles

Increased solar UV radiation could affect terrestrial and aquatic bio-geo-chemical cycles thus

altering both sources and sinks of greenhouse and important trace gases, e.g. carbon dioxide

(CO2), carbon monoxide (CO), carbonyl sulphide (COS), etc. These changes would contribute to

biosphere-atmosphere feedbacks responsible for the atmosphere build-up of these gases. Other

effects of increased UV-B radiation include: changes in the production and decomposition of

plant matter; reduction of primary production changes in the uptake and release of important

atmospheric gases; reduction of bacterioplankton growth in the upper ocean; increased

degradation of aquatic dissolved organic matter (DOM), etc. Aquatic nitrogen cycling can be

affected by enhanced UV-B through inhibition of nitrifying bacteria and photodecomposition of

simple inorganic species such as nitrate. The marine sulphur cycle may also be affected resulting

in possible changes in the sea-to-air emissions of COS and dimethylsulfied (DMS), two gases

that are degraded to sulphate aerosols in the stratosphere and troposphere, respectively.

Effects on Air Quality

Reduction of stratospheric ozone and increased penetration of UV-B radiation result in higher

photodissociation rates of key trace gases that control the chemical reactivity of the troposphere.

This can increase both production and destruction of ozone and related oxidants such as

hydrogen peroxide which are known to have adverse effects on human health, terrestrial plants

and outdoor materials. Changes in the atmospheric concentrations of the hydroxyl radical (OH)

may change the atmospheric lifetimes of important gases such as methane and substitutes of


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chlorofluoro carbons (CFCs). Increased tropospheric reactivity could also lead to increased

production of particulates such as cloud condensation nuclei from the oxidation and subsequent

nucleation of sulphur of both anthropogenic and natural origin (e.g. COS and DMS).

Effects on Materials

Increased levels of solar UV radiation is known to have adverse effects on synthetic polymers,

naturally occurring biopolymers and some other materials of commercial interest. UV-B

radiation accelerates the photodegradation rates of these materials thus limiting their lifetimes.

Typical damages range from discoloration to loss of mechanical integrity. Such a situation would

eventually demand substitution of the affected materials by more photostable plastics and other

materials in future.

In 1974, two United States (US) scientists Mario Molina and F. Sherwood Rowland at the

University of California were struck by the observation of Lovelock that the CFCs were present

in the atmosphere all over the world more or less evenly distributed by appreciable

concentrations. They suggested that these stable CFC molecules could drift slowly upto the

stratosphere where they may breakdown into chlorine atoms by energetic UV-B and UB-C rays

of the sun. The chlorine radicals thus produced can undergo complex chemical reaction

producing chlorine monoxide which can attack an ozone molecule converting it into oxygen andin the process regenerating the chlorine atom again. Thus the ozone destroying effect is catalytic

and a small amount of CFC would be destroying large number of ozone molecules. Their basic

theory was then put to test by the National Aeronautic Space Authority (NASA) scientists and

found to be valid, ringing alarm bells in many countries and laying the foundation for

international action.

Effects on crops

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

important species of plants, such asrice,depend oncyanobacteria residing on their roots for the
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retention ofnitrogen.Cyanobacteria are sensitive to UV light and they would be affected by its

increase.

Public policy

The full extent of the damage that CFCs have caused to the ozone layer is not known and will

not be known for decades; however, marked decreases in column ozone have already been

observed (as explained before).

After a 1976 report by theUnited States National Academy of Sciences concluded that credible

scientific evidence supported the ozone depletion hypothesisa few countries, including the

United States, Canada, Sweden, Denmark, and Norway, moved to eliminate the use of CFCs in

aerosol spray cans. At the time this was widely regarded as a first step towards a more

comprehensive regulation policy, but progress in this direction slowed in subsequent years, due

to a combination of political factors (continued resistance from the halocarbon industry and a

general change in attitude towards environmental regulation during the first two years of the

Reagan administration) and scientific developments (subsequent National Academy assessments

which indicated that the first estimates of the magnitude of ozone depletion had been overly

large). A critical DuPont manufacturing patent for Freon was set to expire in 1979

Chlorofluorocarbon Regulation_and_DuPont.The United States banned the use of CFCs inaerosol cans in 1978. The European Community rejected proposals to ban CFCs in aerosol

sprays, and in the U.S., CFCs continued to be used as refrigerants and for cleaning circuit boards.

Worldwide CFC production fell sharply after the U.S. aerosol ban, but by 1986 had returned

nearly to its 1976 level. In 1993,DuPont shut down its CFC facility.

The U.S. Government's attitude began to change again in 1983, whenWilliam Ruckelshaus

replacedAnne M. Burford as Administrator of theUnited States Environmental Protection

Agency.Under Ruckelshaus and his successor, Lee Thomas, the EPA pushed for an international

approach to halocarbon regulations. In 1985 20 nations, including most of the major CFC

producers, signed theVienna Convention for the Protection of the Ozone Layer which

established a framework for negotiating international regulations on ozone-depleting substances.

That same year, the discovery of the Antarctic ozone hole was announced, causing a revival in
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public attention to the issue. In 1987, representatives from 43 nations signed theMontreal

Protocol.Meanwhile, the halocarbon industry shifted its position and started supporting a

protocol to limit CFC production. The reasons for this were in part explained by "Dr.Mostafa

Tolba,former head of the UN Environment Programme, who was quoted in the 30 June 1990

edition of TheNew Scientist,'...the chemical industry supported the Montreal Protocol in 1987

because it set up a worldwide schedule for phasing out CFCs, which [were] no longer protected

by patents. This provided companies with an equal opportunity to market new, more profitable

compounds.

At Montreal, the participants agreed to freeze production of CFCs at 1986 levels and to reduce

production by 50% by 1999. After a series of scientific expeditions to the Antarctic produced

convincing evidence that the ozone hole was indeed caused by chlorine and bromine frommanmade organohalogens, the Montreal Protocol was strengthened at a 1990 meeting in London.

The participants agreed to phase out CFCs and halons entirely (aside from a very small amount

marked for certain "essential" uses, such asasthma inhalers)by 2000 in non-Article 5 countries

and by 2010 in Article 5 (less developed) signatories. At a 1992 meeting in Copenhagen, the

phase out date was moved up to 1996. At the same meeting, methyl bromide (MeBr), a fumigant

used primarily in agricultural production, was added to the list of controlled substances. It should

be noted that for all substances controlled under the Protocol, phaseout schedules were delayed

for less developed ('Article 5(1)') countries, and phaseout in these countries was supported by

transfers of expertise, technology, and money from non-Article 5(1) Parties to the Protocol.

Additionally, exemptions from the agreed schedules could be applied for under the Essential Use

Exemption (EUE) process for substances other than methyl bromide and under the Critical Use

Exemption (CUE) process for methyl bromide. See Gareauand DeCanio and Norman for more

detail on the exemption processes.

To some extent, CFCs have been replaced by the less damaging hydro-chloro-fluoro-carbons

(HCFCs), although concerns remain regarding HCFCs also. In some applications, hydro-fluoro-

carbons (HFCs)have been used to replace CFCs. HFCs, which contain no chlorine or bromine,

do not contribute at all to ozone depletion although they are potent greenhouse gases. The best

known of these compounds is probably HFC-134a (R-134a), which in the United States has
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largely replaced CFC-12 (R-12)in automobile air conditioners. In laboratory analytics (a former

"essential" use) the ozone depleting substances can be replaced with various other solvents.

Ozone Diplomacy, by Richard Benedick (Harvard University Press, 1991) gives a detailed

account of the negotiation process that led to the Montreal Protocol.Pielke and Betsillprovide an

extensive review of early U.S. government responses to the emerging science of ozone depletion

by CFCs.

More recently, policy experts have advocated for efforts to link ozone protection efforts to

climate protection efforts. Many ODS are also greenhouse gasses, some significantly more

powerful agents of radiative forcing than carbon dioxide over the short and medium term. Policy

decisions in one arena affect the costs and effectiveness of environmental improvements in the

other. Thus many methods have been adopted to prevent the ozone layer depeletion, because of

the implementation of these plans there are seen results that the amount of depletion have

decreased to some extent only, more can be seen if the the reductions of the production of the

fuel burning vehicles that causes more of the depeletion of the ozone layer.

Prospects of ozone depletion
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Although considerable variability in ozone is expected from year to year, including in polar

regions where depletion is largest, the ozone layer is expected to begin to recover in coming

decades due to declining ozone-depleting substance concentrations, assuming full compliance

with the Montreal Protocol.

Temperatures during the Arctic winter of 2006 stayed fairly close to the long-term average until

late January, with minimum readings frequently cold enough to produce PSCs. During the last

week of January, however, a major warming event sent temperatures well above normalmuch

too warm to support PSCs. By the time temperatures dropped back to near normal in March, the

seasonal norm was well above the PSC threshold. Preliminary satellite instrument-generated

ozone maps show seasonal ozone buildup slightly below the long-term means for the Northern

Hemisphere as a whole, although some high ozone events have occurred. During March 2006,the Arctic stratosphere poleward of 60 North Latitude was free of anomalously low ozone areas

except during the three-day period from 17 March to 19 when the total ozone cover fell below

300 DU over part of the North Atlantic region from Greenland to Scandinavia.

The area where total column ozone is less than 220 DU (the accepted definition of the boundary

of the ozone hole) was relatively small until around 20 August 2006. Since then the ozone hole

area increased rapidly, peaking at 29 million km 24 September. In October 2006,NASA

reported that the year's ozone hole set a new area record with a daily average of 26 million km

between 7 September and 13 October 2006; total ozone thicknesses fell as low as 85 DU on 8

October. The two factors combined, 2006 sees the worst level of depletion in recorded ozone

history. The depletion is attributed to the temperatures above the Antarctic reaching the lowest

recording since comprehensive records began in 1979.

On October 2008 theEcuadorian Space Agencypublished a report called HIPERION, a study of

the last 28 years data from 10 satellites and dozens of ground instruments around the world

among them their own, and found that the UV radiation reaching equatorial latitudes was far

greater than expected, climbing in some very populated cities up to 24 UVI, theWHOUV Index

standard considers 11 as an extreme index and a great risk to health. The report concluded that

the ozone depletion around mid latitudes on the planet is already endangering large populations
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could have an impact on the stratospheric ozone layer. In the following year, Crutzen and

(independently) Harold Johnston suggested that NO emissions fromsupersonicaircraft,which

fly in the lower stratosphere, could also deplete the ozone layer.

The Rowland-Molina hypothesis

In 1974Frank Sherwood Rowland,Chemistry Professor at the University of California at Irvine,

and his postdoctoral associateMario J. Molina suggested that long-lived organic halogen

compounds, such asCFCs,might behave in a similar fashion as Crutzen had proposed for nitrous

oxide.James Lovelock (most popularly known as the creator of theGaia hypothesis)had

recently discovered, during a cruise in the South Atlantic in 1971, that almost all of the CFC

compounds manufactured since their invention in 1930 were still present in the atmosphere.

Molina and Rowland concluded that, like N2O, the CFCs would reach the stratosphere where

they would be dissociated by UV light, releasing Cl atoms. (A year earlier, Richard Stolarski and

Ralph Cicerone at the University of Michigan had shown that Cl is even more efficient than NO

at catalyzing the destruction of ozone. Similar conclusions were reached byMichael McElroy

andSteven Wofsy atHarvard University.Neither group, however, had realized that CFCs were a

potentially large source of stratospheric chlorineinstead, they had been investigating thepossible effects of HCl emissions from the Space Shuttle, which are very much smaller.)

The Rowland-Molina hypothesis was strongly disputed by representatives of the aerosol and

halocarbon industries. The Chair of the Board ofDuPont was quoted as saying that ozone

depletion theory is "a science fiction tale...a load of rubbish...utter nonsense".Robert Abplanalp,

the President of Precision Valve Corporation (and inventor of the first practical aerosol spray can

valve), wrote to the Chancellor ofUC Irvine to complain about Rowland's public statements

(Roan, p 56.) Nevertheless, within three years most of the basic assumptions made by Rowland

and Molina were confirmed by laboratory measurements and by direct observation in the

stratosphere. The concentrations of the source gases (CFCs and related compounds) and the

chlorine reservoir species (HCl and ClONO2) were measured throughout the stratosphere, and

demonstrated that CFCs were indeed the major source of stratospheric chlorine, and that nearly
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all of the CFCs emitted would eventually reach the stratosphere. Even more convincing was the

measurement, by James G. Anderson and collaborators, of chlorine monoxide (ClO) in the

stratosphere. ClO is produced by the reaction of Cl with ozoneits observation thus

demonstrated that Cl radicals not only were present in the stratosphere but also were actually

involved in destroying ozone. McElroy and Wofsy extended the work of Rowland and Molina by

showing that bromine atoms were even more effective catalysts for ozone loss than chlorine

atoms and argued that thebrominated organic compounds known ashalons,widely used in fire

extinguishers, were a potentially large source of stratospheric bromine. In 1976 theUnited States

National Academy of Sciences released a report which concluded that the ozone depletion

hypothesis was strongly supported by the scientific evidence. Scientists calculated that if CFC

production continued to increase at the going rate of 10% per year until 1990 and then remain

steady, CFCs would cause a global ozone loss of 5 to 7% by 1995, and a 30 to 50% loss by 2050.

In response the United States, Canada and Norway banned the use of CFCs inaerosol spray cans

in 1978. However, subsequent research, summarized by the National Academy in reports issued

between 1979 and 1984, appeared to show that the earlier estimates of global ozone loss had

been too large.

Crutzen, Molina, and Rowland were awarded the 1995Nobel Prize in Chemistry for their work

on stratospheric ozone.

The ozone hole

The discovery of the Antarctic "ozone hole" byBritish Antarctic Survey scientistsFarman,

Gardiner andShanklin (announced in a paper inNature in May 1985) came as a shock to the

scientific community, because the observed decline in polar ozone was far larger than anyone

had anticipated. Satellite measurements showing massive depletion of ozone around thesouth

pole were becoming available at the same time. However, these were initially rejected as

unreasonable by data quality control algorithms (they were filtered out as errors since the values

were unexpectedly low); the ozone hole was detected only in satellite data when the raw data

was reprocessed following evidence of ozone depletion in in situ observations. When the

software was rerun without the flags, the ozone hole was seen as far back as 1976.
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Susan Solomon,an atmospheric chemist at the National Oceanic and Atmospheric

Administration (NOAA), proposed that chemical reactions onpolar stratospheric clouds (PSCs)

in the cold Antarctic stratosphere caused a massive, though localized and seasonal, increase in

the amount of chlorine present in active, ozone-destroying forms. The polar stratospheric clouds

in Antarctica are only formed when there are very low temperatures, as low as -80 degreesC,

and early spring conditions. In such conditions the ice crystals of the cloud provide a suitable

surface for conversion of unreactive. chlorine compounds into reactive chlorine compounds

which can deplete ozone easily.

Moreover thepolar vortex formed overAntarctica is very tight and the reaction which occurs on

the surface of the cloud crystals is far different from when it occurs in atmosphere. These

conditions have led toozone hole formation in Antarctica. This hypothesis was decisivelyconfirmed, first by laboratory measurements and subsequently by direct measurements, from the

ground and from high-altitude airplanes, of very high concentrations of chlorine monoxide (ClO)

in the Antarctic stratosphere.

Alternative hypotheses, which had attributed the ozone hole to variations in solar UV radiation

or to changes in atmospheric circulation patterns, were also tested and shown to be untenable.

Meanwhile, analysis of ozone measurements from the worldwide network of ground-basedDobson spectrophotometers led an international panel to conclude that the ozone layer was in

fact being depleted, at all latitudes outside of the tropics.These trends were confirmed by satellite

measurements. As a consequence, the majorhalocarbonproducing nations agreed to phase out

production of CFCs, halons, and related compounds, a process that was completed in 1996.

Since 1981 theUnited Nations Environment Programme has sponsored a series of reports on

scientific assessment of ozone depletion,based on satellite measurements. The 2007 report

showed that the hole in the ozone layer was recovering and the smallest it had been for about a

decade.The 2010 report found that "Over the past decade, global ozone and ozone in the Arctic

and Antarctic regions is no longer decreasing but is not yet increasing... the ozone layer outside

the Polar regions is projected to recover to its pre-1980 levels some time before the middle of
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this century... In contrast, the springtime ozone hole over the Antarctic is expected to recover

much later.

Ozone depletion and global warming

There are five areas of linkage between ozone depletion andglobal warming:

Radiative forcing from variousgreenhouse gases and other sources.

The same CO2radiative forcing that produces global warming is expected to cool the

stratosphere.This cooling, in turn, is expected to produce a relative increase inozone

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

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 thetroposphere;the resultingcolder stratosphere emits less long-wave radiation downward, thus cooling the

troposphere. Overall, the cooling dominates; the IPCC concludes that "observed

stratosphericO3losses over the past two decades have caused a negative forcing of the

surface-troposphere system" of about 0.15 0.10wattsper square meter (W/m).
http://en.wikipedia.org/wiki/Global_warminghttp://en.wikipedia.org/wiki/Radiative_forcinghttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Ozonehttp://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Ozonehttp://en.wikipedia.org/wiki/Ozonehttp://en.wikipedia.org/wiki/Ozonehttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/File:Radiative-forcings.svghttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Ozonehttp://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Ozonehttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Radiative_forcinghttp://en.wikipedia.org/wiki/Global_warming


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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 ofgreenhouse gases and ozone depletion since both will lead to

cooling. However, this can be done by numerical stratospheric modeling. Results from

theNational Oceanic and Atmospheric Administration'sGeophysical Fluid Dynamics

Laboratory show that above 20 km (12.4 miles), the greenhouse gases dominate the

cooling.

As noted under 'Public Policy', ozone depleting chemicals are also often 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.

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

testing take decades to 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 aSGI 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

A few of the more common misunderstandings about ozone depletion are addressed briefly here;

more detailed discussions can be found in theozone-depletion FAQ.

CFCs are "too heavy" to reach the stratosphere

It is commonly believed that CFC molecules are heavier than air (nitrogen or oxygen), so that the

CFC molecules cannot reach the stratosphere in significant amount. But atmospheric gases are
http://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administrationhttp://en.wikipedia.org/wiki/Geophysical_Fluid_Dynamics_Laboratoryhttp://en.wikipedia.org/wiki/Geophysical_Fluid_Dynamics_Laboratoryhttp://en.wikipedia.org/wiki/SGI_Origin_2000http://www.faqs.org/faqs/ozone-depletionhttp://www.faqs.org/faqs/ozone-depletionhttp://en.wikipedia.org/wiki/SGI_Origin_2000http://en.wikipedia.org/wiki/Geophysical_Fluid_Dynamics_Laboratoryhttp://en.wikipedia.org/wiki/Geophysical_Fluid_Dynamics_Laboratoryhttp://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administrationhttp://en.wikipedia.org/wiki/Greenhouse_gas


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not sorted by weight; the forces of wind can fully mix the gases in the atmosphere. Despite the

fact that CFCs are heavier than air and with a long lifetime, they are evenly distributed

throughout theturbosphere and reach the upper atmosphere.

Man-made chlorine is insignificant compared to natural sources

Another misconception is that "it is generally accepted that natural sources of tropospheric

chlorine are four to five times larger than man-made one". While strictly true, troposphericchlorine is irrelevant; it is stratospheric chlorine that affects ozone depletion. Chlorine from

ocean spray is soluble and thus is washed by rainfall before it reaches the stratosphere. CFCs, in

contrast, are insoluble and long-lived, allowing them to reach the stratosphere. In the lower

atmosphere, there is much more chlorine from CFCs and relatedhaloalkanes than there is in HCl

from salt spray, and in the stratosphere halocarbons are dominant . Only methyl chloride which

is one of these halocarbons has a mainly natural source ,and it is responsible for about 20 percent

of the chlorine in the stratosphere; the remaining 80% comes from man made sources.

Very violent volcanic eruptions can inject HCl into the stratosphere, but researchershave shown

that the contribution is not significant compared to that from CFCs. A similar erroneous assertion

is that soluble halogen compounds from the volcanic plume ofMount Erebus on Ross Island,

Antarctica are a major contributor to the Antarctic ozone hole.
http://en.wikipedia.org/wiki/Turbospherehttp://en.wikipedia.org/wiki/Salt_sprayhttp://en.wikipedia.org/wiki/Haloalkanehttp://en.wikipedia.org/wiki/Mount_Erebushttp://en.wikipedia.org/wiki/File:Sources_of_stratospheric_chlorine.pnghttp://en.wikipedia.org/wiki/Mount_Erebushttp://en.wikipedia.org/wiki/Haloalkanehttp://en.wikipedia.org/wiki/Salt_sprayhttp://en.wikipedia.org/wiki/Turbosphere


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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 overHalley 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 completely 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.

The ozone hole should be above the sources of CFCs

Some people thought that the ozone hole should be above the sources of CFCs. However, CFCs

are well mixed in thetroposphere and thestratosphere.The reason for occurrence of the ozone

hole above Antarctica is not because there are more CFCs concentrated but because the low

temperatures help form polar stratospheric clouds. In fact, there are findings of significant and

localized "ozone holes" above other parts of the earth.

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

There is a common misconception that ozone hole is really a hole in the ozone layer.When the

"ozone hole" occurs, the ozone in the lower stratosphere is destroyed. The upper stratosphere is

less affected, so that the amount of ozone over the continent decreases by 50 percent or even

more. The ozone hole does not disappear through the layer; on the other hand, it is not a uniform
http://en.wikipedia.org/wiki/G.M.B._Dobsonhttp://en.wikipedia.org/wiki/Halley_Research_Stationhttp://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Halley_Research_Stationhttp://en.wikipedia.org/wiki/G.M.B._Dobson


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'thinning' of the ozone layer. It is a "hole" which is a depression, not in the sense of "a hole in the

windshield."

International Action

The first international action to focus attention on the dangers of ozone depletion in the

stratosphere and its dangerous consequences in the long run on life on earth was focused in 1977

when in a meeting of 32 countries in Washington D.C. a World plan on action on Ozone layer

with UNEP as the coordinator was adopted.

As experts began their investigation, data piled up and in 1985 in an article published in the

prestigious science journal, Nature by Dr. Farman pointed out that although there is overall

depletion of the ozone layer all over the world, the most severe depletion had taken place over

the Antarctica. This is what is famously called as "the Antarctica Ozone hole". His findings were

confirmed by Satellite observations and offered the first proof of severe ozone depletion and

stirred the scientific community to take urgent remedial actions in an international convention

held in Vienna on March 22, 1985. This resulted in an international agreement in 1987 on

specific measures to be taken in the form of an international treaty known as the Montreal

Protocol on Substances That Deplete the Ozone Layer. Under this Protocol the first concrete step

to save the Ozone layer was taken by immediately agreeing to completely phase out

chlorofluorocarbons (CFC), Halons, Carbon tetrachloride (CTC) and Methyl chloroform (MCF)

as per a given schedule

Alternatives to currently used Ozone Depleting Substances

During the last few years intense research has yielded a large number of substitute chemicals as

replacements to currently used chlorofluorocarbons (CFCs), Halons, CTC, and Methyl

chloroform.


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WHAT CAN BE DONE?

Ozone is a natural gas and is naturally replenished over time. This means if we can do something

to balance the natural production with its depletion, there should not be a problem.

Unfortunately, it does not quiet work like that.

People ask if we cannot produce our own ozone gas to replenish what is lost in the stratosphere.

Thats a good question. The sun naturally produces ozone with immense energyand over time.

To do the same, we will be looking at using immense energy too, about twice the energy used in

the USA. That is just not practical.

The only way to do that is to remove the excess chlorine and bromine from the stratosphere. And

the only way to do that is to stop making CFCs and several other chemicals. This is why in the

1990s a meeting of the worlds big nations met and agreed to reduce the usage of CFCs and also

encouraged other nations to do the same. That was decided in the Montreal Protocol.

This is not enough, but at least it was a good starting point. It is always best to talk and discuss

problems than to do nothing at all. This is why learning about Ozone depletion, like you are

doing, is the most important step towards a safe environment in future.

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