ABSTRACT:The ozone layer is essential for protecting society from harmful
UV radiation by acting as a filter. However, this protective layer has been
thinning due to three main sources: human activity, natural sources, and
volcanoes. Human activity is responsible for the most damage to the ozone
layer, thus, society should recognize that much can be done to prevent ozone
layer damage. In 1985, in a region over Antarctica, the yearly polar vortex had
caused the ozone layer to deplete so greatly, that it could be classified as a hole.
In 1996, this hole was large enough to cover Antarctica.
The depletion of the ozone layer does not come without
problems. Scientific research has suggested the probability that increased UV-B
radiation as a result of the thinning ozone layer leads to increased cases of skin
cancer, immuno-suppression, cataracts, and snow blindness due to radiation
damage of the DNA. Additionally, experiments have shown a correlation
between increased UV radiation and crop damage due to UV radiation damaging
the plants DNA. Some scientists, however, feel that this will not be a problem in
the future due to the possibility of breeding UV resistant crops and plants.
Many national governments and agencies recognized the
problem of ozone depletion, and therefore, united in 1987 to sign the Montreal
Protocol. This agreement was implemented to decrease CFC levels in order to
help protect the thinning ozone layer.
Clearly, ozone depletion is a dangerous problem due to
possible disease outbreaks and famine as a result of increased UV-B radiation.
However, society can collectively attempt to combat this problem by relatively
simple means such as education and the practice of ozone smart behavior. For
if society acts now, future generations will be handed a safe and healthy planet.
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1. INTRODUCTION:Atmosphere is the main factor in the world of living
organisms. The balanced condition is maintained on the earth by suggesting and
realizing lost of improved experiments in atmospheric positions. The main and
critical element to which the whole topic is approaching is OZONE layer and the
dependent factors on it. The whole topic is concentrated on ozone and its
concerned branches to which the atmospheric science is related. The conceptual
information is given from resources to effects and their remedies.
The environment is the earth, and you have to help the
earth. The conversation above exhibits the innocence and naiveté of a young
child, who will eventually inherit mother earth, in regards to the ozone layer.
Although the adult reader may chuckle at this young girl’s lack of knowledge, the
average adult is virtually as uneducated. With such a life affecting issue as the
ozone layer, it is essential that society be well informed about the danger ozone
depletion poses to earth.
There are many issues one must explore when educating
himself/herself about the ozone layer. The goal of this paper is to provide the
layman with a general knowledge of important components of ozone education.
First, a general overview will be provided. Next, the reader will learn scientific
aspects of the ozone layer such as factors responsible for ozone depletion, and
then he/she will explore the ozone hole over Antarctica. To continue, societal
aspects that will be addressed include health risks, crop/plant damage, and
organism damage. Finally, actions that government has taken to attempt to
solve the problem will be discussed. The paper will conclude with a discussion of
the importance of ozone education.
2. The ozone layer:The ozone layer is a portion of earth’s atmosphere that
contains high levels of ozone. The atmosphere is divided into five layers: the
troposphere, the stratosphere, the mesosphere, the thermosphere, and the
exosphere. The troposphere is the layer closest to earth and is where all
weather happenings occur. . For a visual of the lowermost three layers of our
atmosphere, refer to Figure 1 below.
The ozone found in our atmosphere is formed by an
interaction between oxygen molecules (composed of two oxygen atoms) and
ultraviolet light. When ultraviolet light hits these oxygen molecules, the reaction
causes the molecules to break apart into single atoms of oxygen.
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 Reactions:-
UV light + O2 --> O + O
2O + 2O2 --> 2O3
These single atoms of oxygen are very reactive, and a
single atom combines with a molecule of oxygen to form ozone (O3), which is
composed of three atoms of oxygen.
Figure 1: Ozone thickness over Labrador, Canada measured in Dobson Units
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The ozone layer is essential for human life. It is able to
absorb much harmful ultraviolet radiation, preventing penetration to the earth’s
surface. Ultraviolet radiation (UV) is defined as radiation with wavelengths
between 290-320 nanometers, which are harmful to life because this radiation
can enter cells and destroy the deoxyribonucleic acid (DNA) of many life forms
on planet earth. In a sense, the ozone layer can be thought of as a ?UV filter? or
our planets ?built in sunscreen? Without the ozone layer, UV radiation would not
be filtered as it reached the surface of the earth would break out and all of the
living civilizations, and all species on earth would be in jeopardy? Thus, the
ozone layer essentially allows life, as we know it, to exist.
In order for scientists to evaluate how much ozone is in
the layer, a unit of measurement called the Dobson Unit is employed. A Dobson
Unit is a measurement of how thick a specific portion of the ozone layer would be
if it were compressed into a single layer at zero degrees Celsius with one unit of
atmospheric pressure acting on it (standard temperature and pressure - STP).
Thus, one Dobson Unit (DU) is defined as .01 mm thickness at standard
temperature and pressure. Figure 2 shows a column of air over Labrador,
Canada. Since the ozone layer over this area would form a 3 mm thick slab, the
measurement of the ozone over Labrador is 300 DU.
 STRIKING FEATURES OF OZONE LAYER:1.natural
balance keeps us well supplied with ozone
:-
Up in the stratosphere, small amounts of ozone are constantly being made by the
action of sunlight on oxygen. At the same time, ozone is being broken down by
natural processes. The total amount of ozone usually stays constant because its
formation and destruction occur at about the same rate.
Human activity has recently changed that natural balance. Certain manufactured
substances (such as chlorofluorocarbons and hydrochlorofluorocarbons) can
destroy stratospheric ozone much faster than it is formed.
2.Ozone is a natural sunblock
Go outside on a fine day and feel the sun warm your face. What happens when a
cloud passes over? You’ll notice that the cloud takes away some of the heat and
light coming from the sun. In much the same way that a cloud blocks the heat on
a hot day, the ozone layer in the stratosphere blocks out the sun’s deadly
ultraviolet rays. It acts as our planet’s natural sunblock.
The sun doesn’t just produce heat and light. It throws out all sorts of other types
of electromagnetic radiation, including ultraviolet radiation (Box 1: Meet the
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ultraviolet family). Because ultraviolet radiation can damage DNA it is potentially
harmful to most living things, including plants (Box 2: Can plants get sunburn?).
Unfortunately our bodies can't detect ultraviolet radiation directly. We can be
unaware of the harm it is doing until it is too late – for example, at the end of a
day in the sun without adequate protection.
3. When there is less ozone in the stratosphere, more ultraviolet
radiation hits us :Even a 1 per cent reduction in the amount of ozone in the upper atmosphere
causes a measurable increase in the ultraviolet radiation that reaches the Earth's
surface. If there was no ozone at all, the amount of ultraviolet radiation reaching
us would be catastrophically high. All living things would suffer radiation burns,
unless they were underground, in protective suits, or in the sea,
4.Ozone-depleting substances usually contain chlorine or bromine
The synthetic chemicals called chlorofluorocarbons (CFCs) are now well-known
as environmental ‘baddies’, even though they are useful and completely nontoxic substances. They get their bad name because they are ozone-eaters
(properly called ozone-depleting substances). CFCs are not the only ozonedepleting substances, but they are the most abundant. Some ozone-depleting
substances are naturally occurring compounds.
Ozone-depleting substances are long-lived because it takes them several years
to drift up into the stratosphere. When they arrive, they are broken apart by
exposure to ultraviolet radiation and that releases the chlorine atoms. These are
the real ozone-killers. The chlorine atoms react with ozone, to form oxygen and
chlorine monoxide.
3.Position of ozone layer:The ozone is present at an altitude in atmosphere,
Mainly in stratosphere from about 12 to 35km.These upper layer of atmosphere
enriched by ozone is commonly known as ozonosphere. The stratosphere is
located directly above the troposphere, about 10-50 kilometers above the planet,
and houses the ozone layer at an altitude of 20-30 kilometers. The mesosphere
is located approximately 50-80 kilometers above the earth, while the
thermosphere rests at an altitude of approximately 100-200 kilometers above the
earth’s surface. Finally, the boundary of the outermost layer, the exosphere,
extends roughly to 960-1000 kilometers above the earth. The presence of ozone
layer in stratosphere for all biota.
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Figure 2: Earth's atmosphere is divided into layers, which have various characteristics.
because it traps (i.e. does not allow to enter.) ,the harmful solar radiations such
as ultraviolet rays .If u.v.radiations reaches the earth surface,then the
temperature of lower atmosphere(i.e. troposphere.) will increase tremendously,
apart from disadvantage of U.V.radiations.
Three forms of oxygen are involved in the ozoneoxygen cycle: Oxygen atoms (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 photo dissociate 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 2 O 2
molecules. It is theorized that prior to the beginning of the depletion trend, the
amount of ozone in the stratosphere was kept roughly constant by a balance
between the rates of creation and destruction of ozone molecules by UV light.
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Ozone loss occurs mainly at the poles :The ozone-destroying reactions take place most
rapidly only under certain conditions in the stratosphere. These conditions –
extreme cold, darkness and isolation, followed by exposure to light – occur over
the polar regions after the long polar winter has finished and the first spring sun
appears.
Antarctica is the worst affected area, probably
because the air above it is most isolated from the rest of the atmosphere).
Scientists often refer to the part of the atmosphere where ozone is most depleted
as the ‘ozone hole’, but it is not really a hole – just a vast region of the upper
atmosphere where there is less ozone than elsewhere.
Ozone-poor air can spread out from the polar
regions and move above other areas. In addition, direct ozone loss elsewhere is
slowly increasing, although it is not occurring at the same rate as over the poles.
4.DESTRUCTION OF OZONE LAYER:1. DEFINITION:Ozone depletion is the result of a complex set of
circumstances and chemistry.
2. OZONE DEPLETION:The term ozone depletion is used to describe two
distinct, but related, observations: a slow, steady decline, of about 3% per
decade, in the total amount of ozone in the earth's stratosphere during the past
twenty years, and a much larger, but seasonal, decrease in stratospheric ozone
over the earth's polar regions during the same period. (The latter phenomenon is
commonly referred to as the "ozone hole".) The detailed mechanism by which the
polar ozone holes form is different from that for the mid-latitude thinning, but the
proximate cause of both trends is believed to be catalytic destruction of ozone by
atomic chlorine and bromine. The primary source of these halogen atoms in the
stratosphere is photo dissociation of chlorofluorocarbon (CFC) compounds,
commonly called Freon’s, and bromofluorocarbon compounds known as Halons,
which are transported into the stratosphere after being emitted at the surface.
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Both ozone depletion mechanisms strengthened as emissions of CFCs and
Halons increased.
It is important to recognize the sources of ozone
depletion before one can fully understand the problem. There are three main
contributors to the ozone problem: human activity, natural sources, and volcanic
eruptions (See Figure 3).
Figure 3: Humans cause more damage to the ozone layer than any other source
Since the ozone layer prevents most harmful UVB
wavelengths (270- 315 nm) of ultraviolet 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 banning the
production of CFCs and halons as well as related ozone depleting chemicals
such as carbon tetrachloride and trichloroethane (also known as methyl
chloroform). It is suspected that a variety of biological consequences, including,
for example, increases in skin cancer, 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. The springtime stratospheric ozone (O3)
layer over the Antarctic is thinning by as much as 50 percent, resulting in
increased midultraviolet (UVB) radiation reaching the surface of the Southern
Ocean. There is concern that phytoplankton communities confined to nearsurface waters of the marginal ice zone will be harmed by increased UVB
irradiance penetrating the ocean surface, thereby altering the dynamics of
Antarctic marine ecosystems. Results from a 6-week cruise (Icecolors) in the
marginal ice zone of the Bellingshausen Sea in austral spring of 1990 indicated
that as the O3 layer thinned: (i) sea surface- and depth-dependent ratios of UVB
irradiance (280 to 320 nanometers) to total irradiance (280 to 700 nanometers)
increased and (ii) UVB inhibition of photosynthesis increased. These and other
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Icecolors findings suggest that O3-dependent shifts of in-water spectral
irradiances alter the balance of spectrally dependent phytoplankton processes,
including photo inhibition, photo reactivation, photo protection, and
photosynthesis. A minimum 6 to 12 percent reduction in primary production
associated with O3 depletion was estimated for the duration of the cruise.
The ozone layer filters out incoming radiation in the
"cell-damaging" ultraviolet (UV) part of the spectrum. Without ozone, life on Earth
would not have evolved the way it has. The discovery of a large ozone hole over
Antarctica and is association with man-made CFCs led the world to take action to
protect the ozone layer.
3.Chemical factors: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·) and atomic chlorine (Cl·) and bromine (Br·). All of these
have both natural and anthropogenic (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 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. Once in the stratosphere, the Cl and Br atoms are liberated
from the parent compounds by the action of ultraviolet light, and can destroy
ozone molecules in a catalytic cycle. In this cycle, a chlorine atom reacts with an
ozone molecule, taking an oxygen atom with it (forming ClO) and leaving a
normal oxygen molecule. A free oxygen atom then takes away the oxygen from
the ClO, and the final result is an oxygen molecule and a chlorine atom, which
then reinitiates the cycle. The chemical shorthand for these reactions are:-
 REACTIONS:-
Cl + O3 → ClO + O2.
ClO + O → Cl + O2.
In sum O3 + O → O2 + O2
For this mechanism to operate there must be a source of O atoms, which is
primarily the photo dissociation of O3
Human activity is by far the most prevalent and
destructive source of ozone depletion, while threatening volcanic eruptions are
less common. Human activity, such as the release of various compounds
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containing chlorine or bromine, accounts for approximately 75 to 85 percent of
ozone damage. Perhaps the most evident and destructive molecule of this
description is chlorofluorocarbon (CFC). CFCs were first used to clean electronic
circuit boards, and as time progressed, were used in aerosols and coolants, such
as refrigerators and air conditioners. When CFCs from these products are
released into the atmosphere, the destruction begins. As CFCs are emitted, the
molecules float toward the ozone rich stratosphere. Then, when UV radiation
contacts the CFC molecule, this causes one chlorine atom to liberate. This free
chlorine then reacts with an ozone (O3) molecule to form chlorine monoxide (ClO)
and a single oxygen molecule (O2). This reaction can be illustrated by the
following chemical equation: Cl + O3 --> O2 + ClO. Then, a single oxygen atom
reacts with a chlorine monoxide molecule, causing the formation of an oxygen
molecule (O2) and a single chlorine atom (O + ClO --> Cl + O2). This threatening
chlorine atom then continues the cycle and results in further destruction of the
ozone layer (See Figure 4). Measures have been taken to reduce the amount of
CFC emission, but since CFCs have a life span of 20-100 years, previously
emitted CFCs will do damage for years to come.
Figure 4: A pictorial explanation of
how
the interaction of CFCs and UV radiation damage the ozone layer.
Natural sources also contribute to the depletion of the ozone layer, but not
nearly as much as human activity. Natural sources can be blamed for
approximately 15 to 20 percent of ozone damage. A common natural source of
ozone damage is naturally occurring chlorine. Naturally occurring chlorine, like
the chlorine released from the reaction between a CFC molecule and UV
radiation, also has detrimental effects and poses danger to the earth. Finally,
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volcanic eruptions are a small contributor to ozone damage, accounting for one
to five percent.
During large volcanic eruptions, chlorine, as a
component of hydrochloric acid (HCl), is released directly into the stratosphere,
along with sulfur dioxide. In this case, sulfur dioxide is more harmful than
chlorine because it is converted into sulfuric acid aerosols. These aerosols
accelerate damaging chemical reactions, which cause chlorine to destroy ozone.
4.Observations: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. Marked decreases in
column ozone in the Antarctic spring and early summer compared to the early
1970s and before have been observed using instruments such as the Total
Ozone Mapping Spectrometer (TOMS).
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5.CREATION OF OZONE HOLE: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 overall cause of ozone depletion is the presence
of chlorine-containing source gases (primarily CFCs and related halocarbons). In
the presence of UVlight, 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).
When the topic of the ozone layer arises, many people
immediately think of the hole over Antarctica, but few know why the hole is
actually there. In 1985, British scientists discovered this hole. A special
condition exists in Antarctica that accelerates the depletion of the ozone layer.
Every Arctic winter, a polar vortex forms over Antarctica. A polar vortex ,a
swirling mass of very cold, stagnant air surrounded by strong westerly winds.
Since there is an absence of sun during Arctic winters, the air becomes incredibly
cold and the formation of ice clouds occurs. When the sun returns in the spring,
the light shining on the nitrogen oxide filled ice particles activates the formation of
chlorine. This excess of ozone destroying chlorine rapidly accelerates the
depletion of the ozone layer. Finally, when the polar vortex breaks up, the rapid
dissolution decreases. It is evident that the effects of the polar vortex are
dramatic. For about two month every southern spring, the total ozone declines by
about 60% over most of Antarctica. In the core of the ozone hole, more than
75% of the ozone is lost and at some altitudes, the ozone virtually disappeared in
October, 1993.The average size of the ozone hole is larger than most continents,
including South America, Europe, Australia, and Antarctica, and the maximum
size of the ozone hole in 1996 was larger than North America (See Figure 5).
Finally, one must note that the hole over Antarctica is truly a hole only in the
Antarctic spring, when the depletion is extremely severe due to thevortex.
During the spring, 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.
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Figure 5: On average, the size of the ozone hole is larger than many countries.
Source: Geocities.com, 1998
The hole above Antarctica has clearly proven to be
detrimental. Plankton, organisms that live on carbon, light, and nutrients such as
nitrogen, are near the bottom of the food chain, and are accustomed to low levels
of UV. In December of 1994, on the island of Bacharcaise off Antarctica,
increased levels of UV radiation decreased the number of photoplankton
dramatically. Photoplankton are the main source of food for krill, which in turn
are the main source of food for various birds and whales in the Antarctic region
As warm, ozone-rich air flows in from lower latitudes, the PSCs are destroyed,
the ozone depletion process shuts down, and the ozone hole heal.Volcanic
eruptions are one of the few natural things that can have a diminishing effect on
the ozone layer. Large eruptions can potentially inject significant quantities of
chlorine (via hydrochloric acid - HCl) directly in the stratosphere where the
highest concentrations of ozone are found
.
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.
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.
Figure 6: Ultraviolet radiation proved detrimental to this Arctic food chain in December,
1994.
At this time, due to the decreased number of phytoplankton, the krill level was so
low that it could not support the penguin population. Thus, some penguins were
forced to travel up to two hundred miles in search of food, but most returned with
none. Furthermore, when summer came, only approximately ten of the 1800
hatched penguin chicks survived. This tragedy illustrates the fact that even
underwater creatures are not protected from harmful UV rays, and is a perfect
example of the entire food chain being affected due to an increase in the UV
radiation as a result of the thinning ozone layer. These polar stratospheric clouds
form during winter, in the extreme cold. Polar winters are dark, consisting of 3
months without solar radiation (sunlight). Not only does lack of sunlight contribute
to a decrease in temperature, but 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 hydrogen chloride
(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 ClONO 2.
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
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homogeneous gas phase reactions, which occurs primarily in the upper
stratosphere.
Warming temperatures near the end of spring break up the vortex around midDecember. As warm, ozone-rich air flows in from lower latitudes, the PSCs are
destroyed, the ozone depletion process shuts down, and the ozone hole
heal.Volcanic eruptions are one of the few natural things that can have a
diminishing effect on the ozone layer. Large eruptions can potentially inject
significant quantities of chlorine (via hydrochloric acid - HCl) directly in the
stratosphere where the highest concentrations of ozone are found. However, the
vast majority of volcanic eruptions are too weak to reach the stratosphere,
beginning approximately 12 km above the Earth' surface. Thus, any HCl emitted
during a smaller eruption remains in the lowest atmosphere where it is quickly
dissolved and washed out by rain. In contrast man-made CFCs do not dissolve in
water and can therefore reach the stratosphere through atmospheric mixing.
It is also possible that ice particles containing sulphuric acid from large volcanic
eruptions may contribute to ozone loss. When chlorine compounds resulting from
the breakup of man-made CFCs in the stratosphere are present, the sulphate
particles serve to convert them into more active forms that may cause more rapid
ozone depletion. In 1991 Mt. Pinatubo in the Philippines erupted tonnes of dust
and gas high into the atmosphere which caused global reductions in the ozone
layer for 2 to 3 years. Thus, whilst large volcanic eruptions may increase the rate
of stratospheric ozone depletion, it is more probable that the presence of chlorine
from man-made CFC emissions is the chief cause of ozone loss in the first
instance.
6.SOURCES OF OZONE DEPLETION:The distribution of ozone in the stratosphere is a
function of altitude, latitude and season. It is determined by photochemical and
transport processes. The ozone layer is located between 10 and 50 km above
the Earth's surface and contains 90% of all stratospheric ozone. Under normal
conditions, stratospheric ozone is formed by a photochemical reaction between
oxygen molecules, oxygen atoms and solar radiation. The ozone layer is
essential to life on earth, as it absorbs harmful ultraviolet-B radiation from the
sun. In recent years the thickness of this layer has been decreasing, leading in
extreme cases to holes in the layer. Measurements carried out in the Antarctic
have shown that at certain times, more than 95% of the ozone concentrations
found at altitudes of between 15 and 20 km and more than 50% of total ozone
are destroyed, with reductions being most pronounced during winter and in early
spring. Natural phenomena, such as sun-spots and stratospheric winds, also
decrease stratospheric ozone levels, but typically not by more than 1-2%.
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The main cause of ozone layer depletion is the increased stratospheric
concentration of chlorine from industrially produced CFCs , halons and selected
solvents. Once in the stratosphere, every chlorine atom can destroy up to 100
000 ozone molecules. The amount of damage that an agent can do to the ozone
layer is expressed relative to that of CFC-11 and is called the Ozone Depletion
Potential (ODP), where the ODP of CFC-11 is 1.
The lifetime of some of these ozone depleting substances is very long, and they
may continue to deplete the ozone layer long after their use has been phased
out. In this publication the ODP values for 100-year timespan are used.
Nevertheless some shorter-lived substances may have a very high chlorine
loading potential and thus their effect in the short term is much larger than
reflected by their ODP value.
Aircraft emissions of nitrogen oxides and water vapour add to this depletion
effect by creating ice crystals that serve as a base for ozone destroying
reactions.
The main potential consequences of this ozone depletion are:




increase in UV-B radiation at ground level: a one percent loss of ozone
leads to a two percent increase in UV radiation. Continuous exposure to
UV radiation affects humans, animals and plants, and can lead to skin
problems (ageing, cancer), depression of the immune system, and corneal
cataracts (an eye disease that often leads to blindness). Increased UV
radiation may also lead to a massive die-off of photoplancton (a CO 2
"sink") and therefore to increased global warming.
disturbance of the thermal structure of the atmosphere, probably resulting
in changes in atmospheric circulation;
reduction of the ozone greenhouse effect: ozone is considered to be a
greenhouse gas. A depleted ozone layer may partially dampen the
greenhouse effect. Therefore efforts to tackle ozone depletion may result
in increased global warming.
changes in the tropospheric ozone and in the oxidising capacity of the
troposphere.
 Resource Depletion :In 1972, the first report to the Club of Rome, "The Limits to Growth", was
published. It marked the beginning of modern environmental policy. The report
highlighted the impossibility of sustaining exponential economic growth and its
associated Resource Depletion. Many of the resources that drive our economies
are limited and will therefore one day be exhausted, if we continue to use them at
current rates.
Twenty-five years after "Limits to Growth," the focus of environmental policy has
shifted to other policy fields. For example, we have realised that, in spite of fairly
abundant world resources of coal, the limits imposed by the risks of Climate
Change will not allow their full exploitation.
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Nonetheless, the threat of Resource Depletion remains. The emphasis given to
mineral oil during the first and second "oil crises" has been replaced by a wider
picture of resources including (in the order of importance expressed by the expert
panel) groundwater, energy, land, fertile soil, forests and fish stocks. One aspect
which these resources have in common is that their depletion may have
important economic repercussions. For example, consumer prices for certain fish
species have increased drastically, due to their over-exploitation. The same can
be observed, at least in parts of the European Union, for the prices of land and
tap water.
Some experts include biodiversity in their list of resources. However, Loss of
Biodiversity is an independent policy field, that is treated explicitly in Agenda 21
and in the Fifth Environmental Action Programme under the title "Protection of
Nature and Biodiversity." The main reason for this distinction is probably the
dominant role of ethical aspects in the biodiversity debate, which would make a
comparison to the more economically relevant resources treated here very
difficult.
The indicators presented in this chapter portray the use of some key resources
by the citizens of the European Union. In contrast to many other pressure
indicators, their message is relatively clear and non-controversial. Further
development will focus on improving data quality and coverage, on links to
economic indicators such as prices of these resources, and on exploring the
potential to aggregate these indicators to an overall resource depletion index
based for example on their economic value, their proven reserves, or their
strategic importance for the world economy.
a. CFCs are "too heavy" to reach the stratosphere:A frequent point made is that since CFC molecules are
much heavier than nitrogen or oxygen, they cannot reach the stratosphere in
significant quantities. But atmospheric gases are not sorted by weight; the forces
of wind (turbulence) are strong enough to fully intermix gases in the atmosphere.
A loss of ozone in the stratosphere because of mankind's pollution with ozone
depleting chemicals such as CFCs will increase the amount of UV radiation that
reaches the Earth's surface. As a consequence, health disorders, damage to
plant and aquatic life, and degradation of materials will probably increase. Ozone
depletion may even affect the global climate.
Whilst increases of UV radiation may affect the
production and removal of carbon dioxide, the main greenhouse gas, ozone
depletion itself can influence the global climate. Ozone is also a greenhouse gas,
and as well as filtering out the incoming UV radiation from the Sun, can trap
much of the infrared (IR) heat trying to escape the Earth to space. If stratospheric
ozone is destroyed, ozone’s contribution to the greenhouse effect is reduced.
This could offset some of the global warming due to man-made emissions of
carbon dioxide, methane and nitrous oxide.
16
Human activity is by far the most prevalent and
destructive source of ozone depletion, while threatening volcanic eruptions are
less common. Human activity, such as the release of various compounds
containing chlorine or bromine, accounts for approximately 75 to 85 percent of
ozone damage. Perhaps the most evident and destructive molecule of this
description is chlorofluorocarbon (CFC). CFCs were first used to clean electronic
circuit boards, and as time progressed, were used in aerosols and coolants, such
as refrigerators and air conditioners. When CFCs from these products are
released into the atmosphere, the destruction begins. As CFCs are emitted, the
molecules float toward the ozone rich stratosphere. Then, when UV radiation
contacts the CFC molecule, this causes one chlorine atom to liberate. This free
chlorine then reacts with ozone (O3) molecule to form chlorine monoxide (ClO)
and a single oxygen molecule (O2). This reaction can be illustrated by the
following chemical equation: Cl + O3 --> O2 + ClO. Then, a single oxygen atom
reacts with a chlorine monoxide molecule, causing the formation of an oxygen
molecule (O2) and a single chlorine atom (O + ClO --> Cl + O2). This threatening
chlorine atom then continues the cycle and results in further destruction of the
ozone layer (See Figure 4). Measures have been taken to reduce the amount of
CFC emission, but since CFCs have a life span of 20-100 years, previously
emitted CFCs will do damage for years to come.
CFCs Smuggling:As a result of the decline in the production and use of
CFCs, and the continuation of CFC production in developing countries (allowed
under the provisions of the Montreal Protocol until 2010), the lure of illegal trade
in CFCs is obvious. Significant volumes of illegal imports of CFCs into Western
Europe have been reported, even though production in Western Europe ceased
at the end of 1994. The Montreal Protocol currently does not require Parties to it
to implement controls against illegal trade. However, the eighth meeting of the
Conference of Parties, held in November 1996 in Costa Rica, urged countries to
install verification programs to reduce illegal trade in ozone-depleting
substances.
Ironically, as the ozone layer gradually repairs itself
during the
century, this cooling potential will be lost. More significantly, the
replacement chemicals to CFCs, the HCFCs, which themselves do little harm to
the ozone layer, are very strong greenhouse gases, and are further contributing
to the potential problem of global warming.Chlorofluorocarbons (CFCs) are highly
stable compounds that are used as propellents in spray cans and in refrigeration
units. They are several organic compounds composed of carbon, fluorine,
chlorine, and hydrogen. CFCs are manufactured under the trade name Freon
(q.v.).
21st
17
Developed during the 1930s, CFCs found wide application after World War II.
These halogenated hydrocarbons, notably trichlorofluoromethane (CFC-11, or F11) and dichlorodifluoromethane (CFC-12, or F-12), have been used extensively
as aerosol-spray propellants, refrigerants, solvents, and foam-blowing agents.
They are well-suited for these and other applications because they are nontoxic
and nonflammable and can be readily converted from a liquid to a gas and vice
versa.
Chlorofluorocarbons or CFCs (also known as Freon)
are non-toxic, non-flammable and non-carcinogenic. They contain fluorine atoms,
carbon atoms and chlorine atoms. The 5 main CFCs include CFC-11
(trichlorofluoromethane - CFCl3), CFC-12 (dichloro-difluoromethane - CF2Cl2),
CFC-113
(trichloro-trifluoroethane
C2F3Cl3),
CFC-114
(dichlorotetrfluoroethane - C2F4Cl2), and CFC-115 (chloropentafluoroethane - C2F5Cl).
CFCs have been found to pose a serious environmental
threat. Studies undertaken by various scientists during the 1970s revealed that
CFCs released into the atmosphere accumulate in the stratosphere, where they
had a deleterious effect on the ozone layer. Stratospheric ozone shields living
organisms on Earth from the harmful effects of the Sun's ultraviolet radiation;
even a relatively small decrease in the stratospheric ozone concentration can
result in an increased incidence of skin cancer in humans and in genetic damage
in many organisms. In the stratosphere the CFC molecules break down by the
action of solar ultraviolet radiation and release their constituent chlorine atoms.
These then react with the ozone molecules, resulting in their removal. CFCs have
a lifetime in the atmosphere of about 20 to 100 years, and consequently one free
chlorine atom from a CFC molecule can do a lot of damage, destroying ozone
molecules for a long time. Although emissions of CFCs around the developed
world have largely ceased due to international control agreements, the damage
to the stratospheric ozone layer will continue well into the 21st century.
b. Manmade chlorine is insignificant compared to natural: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.
The chlorine from ocean spray is in the form HCl and is soluble; it never reaches
the stratosphere. Another point to note when evaluating the contributions of
various gases to stratospheric ozone is that methyl chloride.
18
Molecules only contribute a single chlorine atom, but
CFC molecules contribute multiple chlorine atoms. Very large volcanic eruptions
can inject HCl directly into the stratosphere, but direct measurements have
shown that their contribution is small compared to that of chlorine from CFCs.
c. Nox:The supersonic aircrafts fly at ozonosphere
cruising altitudes and exhaust directly water vapour and NOX into the
atmosphere. Similarly, nuclear explosions produce large quantities of NOX which
directly enter into stratosphere. Following between O3 and NOX are
predetermining.
 REACTIONS:-
NO + O3 → NO2 + O2
NO2 + O3 → NO3 + O2
H2O → OH + H
H + O3 → OH + O2
19
Species of molecules such as NO3, OH and NO2 are highly reactive but may
have relatively long time. The net result is that NOX increases the rate of O3
destruction with no change in conc. of NO. This catalytic cycle could go on
indefinitely causing reduction of large the conc. of NO.
7. EFFECTS:The Montreal Protocol on Substances that Deplete
the Ozone Layer requires periodic assessments of available scientific,
environmental, technical and economic information. The assessments shall be
made at least every four years. Assessments were made in 1989, 1991, 1994,
and the present one, in 1998. The 1998 assessment focuses on new information
since 1994, but it includes some background of prior information, so that it can be
read without having the earlier reports at hand. In 1994, the ozone layer was
predicted to become thinner until about 1998, and to recover gradually thereafter.
Taking into account new information, the Atmospheric Science Panel now
expects that the most vulnerable period for ozone depletion will be extended into
the coming two decades. Scientific studies are continuing on the most important
effects, and on what can be done to prevent or mitigate these.
The present assessment deals with the results of such
investigations. These repeatedly give reasons for concern for potential effects,
but relatively little progress has been made in quantifying these effects. The more
the investigators look into the problems, the more the complexity becomes
apparent. Nevertheless, the knowledge is accumulating.
a. Increased UV due to the ozone hole:
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 radioactive transfer model calculations, but cannot be calculated from
direct measurements. The springtime stratospheric ozone (O3) layer over the
Antarctic is thinning by as much as 50 percent, resulting in increased
midultraviolet (UVB) radiation reaching the surface of the Southern Ocean. There
is concern that phytoplankton communities confined to near-surface waters of the
marginal ice zone will be harmed by increased UVB irradiance penetrating the
ocean surface, thereby altering the dynamics of Antarctic marine ecosystems.
Results from a 6-week cruise (Icecolors) in the marginal ice zone of the
20
Bellingshausen Sea in austral spring of 1990 indicated that as the O3 layer
thinned: (i) sea surface- and depth-dependent ratios of UVB irradiance (280 to
320 nanometers) to total irradiance (280 to 700 nanometers) increased and (ii)
UVB inhibition of photosynthesis increased. These and other Icecolors findings
suggest that O3-dependent shifts of in-water spectral irradiances alter the
balance of spectrally dependent phytoplankton processes, including photo
inhibition, photo reactivation, photoprotection, and photosynthesis. A minimum 6
to 12 percent reduction in primary production associated with O3 depletion was
estimated for the duration of the cruise.
b. Biological effects of increased UV:The main public concern regarding the ozone hole has been the
effects of surface UV on human health. 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. UVB (the higher energy UV radiation absorbed by ozone) is
generally accepted to be a contributory factor to skin cancer. The most common
forms of skin cancer in humans, basal and squalors cell carcinomas, have been
strongly linked to UVB exposure. The mechanism by which UVB induces these
cancers is well understood — absorption of UVB radiation causes the pyramiding
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%.
One study showed that a 10% increase in UVB
radiation was associated with a 19% increase in melanomas for men and 16%
for women. An increase of UV radiation would also 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 very
sensitive to UV light and they would be affected by its increase.
 CHANGES IN BIOLOGICALLY ACTIVE ULTRAVIOLET
RADIATION REACHING THE EARTH'S SURFACE:Stratospheric ozone levels are near their lowest point
since measurements began, so current UV-B radiation levels are thought to be
close to their maximum. Total stratospheric content of ozone-depleting
substances is expected to reach a maximum before the year 2000. All other
things being equal, the current ozone losses and related UV-B increases should
be close to their maximum. Increases in surface erythemal UV radiation relative
to
the
values
in
the
1970s
are
estimated
to
be:
21
- about 7% at Northern Hemisphere mid-latitudes in winter/spring;
- about 4% at Northern Hemisphere mid-latitudes in summer/fall;
- about 6% at Southern Hemisphere mid-latitudes on a year-round basis;
about
130%
in
the
Antarctic
in
spring;
and
- about 22% in the Arctic in spring.
Reductions in atmospheric ozone are expected to result
in higher amounts of ultraviolet-B (UV-B) radiation reaching the Earth's surface.
The expected correlation between increases in surface UV-B radiation and
decreases in overhead ozone has been further demonstrated and quantified by
ground-based instruments under a wide range of conditions. Improved
measurements of UV-B radiation are now providing better geographical and
temporal coverage. Surface UV-B radiation levels are highly variable because of
cloud cover, and also because of local effects including pollutants and surface
reflections. These factors usually decrease atmospheric transmission and
therefore the surface irradiances at UV-B as well as other wavelengths.
Occasional cloud-induced increases have also been reported.
With a few exceptions, the direct detection of UV-B trends at low and midlatitudes remains problematic due to this high natural variability, the relatively
small ozone changes, and the practical difficulties of maintaining long-term
stability in networks of UV-measuring instruments. Few reliable UV-B radiation
measurements are available from pre-ozone depletion days. Satellite-based
observations of atmospheric ozone and clouds are being used, together with
models of atmospheric transmission, to provide global coverage and long-term
estimates of surface UV-B radiation.Estimates of long term (1979-1992) trends in
zonally-averaged UV-irradiances that include cloud effects are nearly identical to
those for clear-sky estimates, providing evidence that clouds have not influenced
the UV-B trends. However, the limitations of satellite-derived UV estimates
should be recognized. To assess uncertainties inherent in this approach,
additional validations involving comparisons with ground-based observations are
required.
Direct comparisons of ground-based UV-B radiation
measurements between a few mid-latitude sites in the Northern and Southern
Hemispheres have shown larger differences than those estimated using satellite
data. Ground-based measurements show that summertime erythemal UV
irradiances in the Southern Hemisphere exceed those at comparable latitudes of
the Northern Hemisphere by up to 40%, whereas corresponding satellite-based
estimates yield only 10 to 15% differences. Atmospheric pollution may be a factor
in this discrepancy between ground-based measurements and satellite-derived
estimates. UV-B measurements at more sites are required to determine whether
the larger observed differences are globally representative. High levels of UV-B
radiation continue to be observed in Antarctica during the recurrent spring-time
ozone hole.For example, during ozone hole episodes, measured biologicallydamaging radiation at Palmer Station, Antarctica (64°S) has been found to
22
approach and occasionally even exceed maximum summer values at San Diego,
USA (32°N).
Long term predictions of future UV-B levels are difficult and uncertain.
Nevertheless, current best estimates suggest that a slow recovery to pre-ozone
depletion levels may be expected during the next half-century. Although the
maximum ozone depletion, and hence maximum UV-B increase, is likely to occur
in the current decade, the ozone layer will continue to be in its most vulnerable
state into the next century. The peak depletion and the recovery phase could be
delayed by decades because of interactions with other long-term atmospheric
changes, e.g. increasing concentrations of greenhouse gases. Other factors that
could influence the recovery include non-ratification and/or non-compliance with
the Montreal Protocol and its Amendments and Adjustments, and future volcanic
eruptions. The recovery phase for surface UV-B irradiances will probably not be
detectable until many years after the ozone minimum
c.Impacts health:As temperatures rise from global warming ,the
frequency and severity of heat wa ves will grow –as will the potential for bad air
days.The risk of illness and death due to dehydration,heat attack,stroke ,and
respiratry disease will increase as a a a result.Those most likely to suffer are
children,the elderly ,and other vulnerable populations.
The health risks associated with ozone depletion will
principally be those due to increased ultraviolet B radiation (UV-B) in
environment, i.e., increased damage to the eyes, the immune system and the
skin. Some new risks may also be introduced with the increased use of
alternatives to the ozone-depleting substances (ODSs). Quantitative risk
estimates are available for some of the UV-B-associated effects, e.g., cataract
and skin cancer; however the data are insufficient to develop similar estimates
for effects such as immunosuppression and the toxicity of alternatives. Ocular
damage from UV exposures includes effects on the cornea, lens, iris and
associated epithelial and conjunctival tissues. The most common acute ocular
effect of environmental ultraviolet radiation (UVR) is photokeratitis. Also known
as snowblindness in skiers, this condition also occurs in other outdoor
recreationists. Chronic eye conditions likely to increase with ozone depletion
include cataract, squamous cell carcinoma, ocular melanoma and a variety of
corneal/conjunctival effects, e.g., pterygium and pinguecula.
Suppression of local (at the site of UV exposure) and
systemic (at a distant, unexposed site) immune responses to a variety of
antigens has been demonstrated in both humans and animals exposed to UV-B.
In experiments with animals these effects have been shown to worsen the
course/outcome of some infectious diseases and cancers. There is reasonably
good evidence that such immunosuppression plays a role in human
23
carcinogenesis; however, the implications of such immunosuppression for human
infectious diseases are still unknown. In light-skinned populations, exposure to
solar UVR appears to be the most important environmental risk factor for basal
and squamous cell carcinomas and cutaneous melanoma. Originally it was
believed that total accumulated exposure to UVR was the most important
environmental factor in determining risk for these tumors. Recent information
now suggests, that only squamous cell carcinoma risk is related to total
exposure. In the cases of both basal cell carcinoma and melanoma, new
information suggests that increases in risk are tied to early exposures (before
about age 15), particularly those leading to severe sunburns.
Testing of a number of the CFC alternatives indicates
that most of these chemicals have low acute toxicity, and low to moderate
chronic toxicity. Some chemicals that were originally proposed as alternatives
have been dropped from consideration because these tests raised concerns
about toxicity and/or manufacturing difficulties. In one instance, high accidental
occupational exposure was associated with liver damage, underlining the need
for care in the use of these substitutes. Recent quantitative risk estimates have
been developed for cataract, melanoma and all skin cancers combined. These
estimates indicate that under the Montreal adjustments cataract, and skin cancer
incidence will peak mid-century at an additional incidence of just under 3 per
100,000 and about 7 per 100,000, respectively. Every year, there are between
two and three million new cases of non-malignant melanomas and more than
130 000 new melanoma skin cancer cases worldwide. An estimated 66 000
deaths occur annually from melanoma and other skin cancers.The cause of
many of these skin cancers is ultraviolet radiation (UV) from the sun. Children,
who are both most vulnerable and most exposed, are disproportionately affected.
In response to the problem, the World Health Organization (WHO), the United
Nations Environment Programmer (UNEP) and other partners in the Intersun
Project are launching a set of new educational materials today.
The new package will help children, their families and
educators protect children from the risks of developing malignant and nonmalignant skin cancers, cataracts and other UV-caused conditions.The materials
support recommendations made in "Sun Protection, An Essential Element of
Health-Promoting Schools", a part of the WHO Information Series on School
Health. "As ozone depletion becomes more marked and as people around the
world engage more in sun-seeking behaviour, the risk of developing health
complications from over-exposure to UV radiation is becoming a substantial
public health concern," said WHO Director General Dr Lee Jong-wook at WHO’s
Geneva, Switzerland Headquarters."Recent scientific findings have shown that
the ozone layer is on the road to recovery, but we must remain vigilant and more
needs to be done before we can say that the problem is solved for good," said
Klaus Toepfer, UNEP’s Executive Director."The phase-out of the ozone depleting
pesticide Methyl Bromide, combating the illegal trade in CFCs and full
implementation of the Montreal Protocol in developing countries are all issues
24
that need to be tackled. Only then can we say that the sky above our heads will
be safe for our children and their children to come.""UV radiation is of particular
concern because people are often unaware of the health risks. The effects of
exposure often do not appear until many years later and over-exposure to the
sun poses a risk to all populations, not just fair-skinned ones," said Dr Mike
Repacholi, Coordinator of WHO’s Radiation and Environmental Health Unit.To
help people around the world become more aware of the risks from exposure to
UV radiation, and to take the measures to prevent over-exposure, WHO’s
Intersun Project is today launching a School Sun Protection Package. The
Package comprises three booklets: a guide for schools and teachers on why and
how to develop effective sun education programmes, practical teaching materials
for primary school students, and evaluation materials to assess the effectiveness
of primary school sun-education programmes.
"We know that by reducing over-exposure of children
and adolescents to the sun, we can substantially reduce the risk of contracting
skin cancers, cataracts and other conditions which might only appear much later
in life. As a significant part of a person’s lifetime exposure to UV comes before
the age of 18, it is obvious that educating children and young people about the
dangers of UV exposure is key to preventing the consequences of this, and
school programmes have been shown to be the most effective way of reaching
and educating children," said Dr Lee."While most of the known melanomas
included in the International Agency for Research on Cancer (IARC) statistics
occur in the industrialized world, this is not necessarily because only fair-skinned
populations are affected by UV radiation. Given adequate reporting mechanisms,
we would expect to see many more melanoma cases originating in developing
countries. Moreover cataract susceptibility has nothing to do with the skin type
and people living close to the equator are most likely to be affected," added Dr
Repacholi.Cataracts are responsible for more than eight million DisabilityAdjusted Life Years worldwide; a comparative risk assessment to estimate the
burden of disease attributable to UV radiation is currently under way to try and
estimate how many of these cataracts are attributable to sun exposure.
The effect of ozone depletion on human health has
been a major focus of scientists since the concern about the damage to the
ozone layer was first given international prominence in 1972.In March 1977, the
"World Plan of Action on the Ozone Layer" was adopted under the auspices of
the United Nations Environmental Programme (UNEP). This plan called for,
amongst other things, research into the effect of ozone depletion on human
health.Owing to increasing concern over the continuing depletion of the ozone
layer and its possible long-term consequences to all forms of life, the "Vienna
Convention for the Protection of the Ozone Layer" was adopted by the
international community in March 1985. This was followed in September 1987
with agreement on specific measures to be taken to arrest the decline under the
"Montreal Protocol on Substances that Deplete the Ozone Layer."
25
Since 1997 several reports have been presented by international scientists on
the effects of ozone depletion on human health. The consensus is that depletion
of the ozone layer leads to significant increases in ultra-violet-B radiation (UV-B)
reaching the Earth's surface. This excessive UV-B is responsible for a wide
range of potentially damaging human and animal health effects, primarily related
to skin, eyes and immune system.Small quantities of ultraviolet-B radiation (UVB) are essential to human health, acting as a catalyst in the generation of vitamin
D. However, large amounts of UV-B are harmful to a wide range of biological
systems. One of the deleterious effects of UV-B on human beings is related to
prolonged, deliberate , as well as inadvertent sunlight exposure, which leads to
the development of non-melanoma skin cancer and malignant melanoma of the
skin. This is particularly applicable to fair-skinned persons who sunburn easily
and who receive prolonged occupational or recreational exposure. Studies have
shown that in Europe persons who are now age 30 have a higher incidence of
melanoma than persons at age 30, ten years earlier. It is estimated that a onepercent decrease in stratospheric ozone will result in a three-percent increase in
non-melanoma skin cancer, and a lower but sill significant increase in
melanoma.Another deleterious effect of UV-B is damage to both the cornea and
lens of the eye. The initial response of the eye to exposure to UV-B radiation is
the condition termed photokeratitis in which the front of the eye, the eyelids and
the skin surrounding the eyes become reddened.Cataract, a disease of the lens
is the most prevalent form of ocular damage associated with UV exposure.
Corrective surgery can prevent most cataracts from causing blindness. However,
in the United States, cataract remains the third leading cause of legal blindness.
In developing countries, where the percentage of the World aged population is
greatest and where such operations are not always available, cataracts result in
a much higher incidence of blindness and can become a major public health
problem. It has been estimated that a one-percent decrease in stratospheric
ozone will be accompanied by a 0.6 to 0.8 percent increase in cataracts.
Ultraviolet radiation is known to affect the
immunological defenses of the skin. The skin often is the first point of contact
with many foreign substances (antigens) including infectious agents. In these
instances, the skin's immune response is the body's first line of defense.
Preliminary experiments of infectious diseases using animal models have
indicated that UV-B can also adversely affect the ability of animals to respond to
or contain various infectious agents. Although there are as yet no epidemiological
data to suggest that such effects occur in human populations, nevertheless,
animal data suggest that an increase in the severity of certain infections may
occur as UV-B increases due to ozone depletion.In areas of the world where
such infections already pose a significant challenge to the public health care
delivery systems, the added effect due to ozone depletion may be
significant.Trinidad and Tobago as a signatory to the Montreal Protocol for the
Protection f the Ozone Layer, is determined and committed to doing its part to
reduce and ultimately eliminate the use of ozone depleting substances (ODS).To
26
this end, the country has targeted the air-conditioning sector in tits efforts to
reduce Chlorofluoro-carbons (CFCs), an ozone depleting substance.
d.Extreme heats;If global warming continues unabated,causing temperatures to rise into the
higher warming range, statewide summer temperature in california are projected
to rise as much as 9 to 18 degree F,heat waves will become more common and
more severe,and the noof days with temperatures above 90 degree in Los
Angeles and 95 degree F .
8.WASTEGES:As a result of economic growth, waste from all sources has
increased dramatically over the last decades. The waste management sector, in
charge of waste treatment and disposal, has become an independent economic
sector, as waste management becomes an environmental problem of growing
concern.
Hazardous and non-hazardous waste present risks to the environment. The
environmental impacts that have been most closely associated with waste
management are, for example:




greenhouse effect (e.g. methane emissions from landfill sites),
pollution of ground and surface water,
soil contamination,
additional health impacts from odour, noise (e.g. waste transport) and
nature deterioration.
Moreover, the proper treatment of waste is an economic burden on industry,
municipalities and households and creates in itself secondary waste – mostly
hazardous waste.
One of the key tasks for the 1990s, as outlined in the Fifth Environmental Action
Programmed, is to halt and reverse current trends in waste generation, in terms
of both volume increase and environmental hazard and damage. The European
Union's strategy for waste management, Council Resolution of 7 May 1990,
focused on prevention, reuse, promotion of recovery, minimization of final
disposal, regulation of transport and remedial action.
A major influence on the waste management policies of Member States has been
the Basle Convention on the control of Tran boundary movements of hazardous
waste and their disposal. The Convention requires generation and transponder
flows to be reported, for different types of hazardous waste, as laid down in the
Annexes 1 and 2 of the Convention. A further development of the Convention
27
introduced a ban on exports of hazardous waste to non-OECD countries. This
was transposed into Community legislation by Council Regulation.
Chapter 20 of Agenda 21 titled "Environmentally sound
management of hazardous waste" is also followed under the EU waste strategy
and related legislation. Compilation of waste statistics at Community level has
shown that the data in the Member States are very heterogeneous. A statistical
methodology was proposed in order to remedy this situation, including a system
of statistical surveys in industry, local authorities and the processing sector. The
proposed methodology was tested via four pilot studies undertaken by Denmark,
the Netherlands, Portugal and the United Kingdom. The main conclusion was
that a common classification system is crucial for the comparability of data
between Member States.
9.FUTURE PROSPECTS OF O.D.:A 2005 IPCC summary of ozone issues observed that
observations and model calculations suggest that the global average amount of
ozone depletion has now approximately stabilized. 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 normal — much 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 Greenland to Scandinavia.
Since the adoption and strengthening of the Montreal
Protocol has led to reductions in the emissions of CFCs, atmospheric
concentrations of the most significant compounds have been declining. These
substances are being gradually removed from the atmosphere. By 2015, the
Antarctic ozone hole should have reduced by only 1 million km 2 out of 25
(Newman et al., 2004); complete recovery of the Antarctic ozone layer will not
occur until the year 2050 or later. Work has suggested that a detectable (and
statistically significant) recovery will not occur until around 2024, with ozone
levels recovering to 1980 levels by around 2068 (Newman et al., 2006).
There is a slight caveat to this, however. Global
warming from CO2 is expected to cool the stratosphere. Even though the
stratosphere as a whole is cooling, high-latitude areas may become increasingly
predisposed to springtime stratospheric warming events as weather patterns
change in response to higher greenhouse gas loading. This would cause PSCs
to disappear earlier in the season, and may explain why Antarctic ozone hole
seasons have tended to end somewhat earlier since 2000 as compared with the
most prolonged ozone holes of the 1990s.
The decrease in ozone-depleting chemicals has also
been significantly affected by a decrease in bromine-containing chemicals. The
28
data suggest that substantial natural sources exist for atmospheric methyl
bromide (CH3Br).
With a clear understanding of these uncertainties, it is nevertheless of interest
to examine the implications of current international regulations to the future of the
ozone layer, and consequently to the future of UV radiation. The 1987 Montreal
Protocol and its subsequent adjustments and amendments limit the production
and emission of ozone-destroying substances, primarily halocarbons. The
atmospheric concentrations of these chemicals had been increasing throughout
the 1970s and 1980s, but observations in the last few years (e.g. Montzka et al.,
1996) show a marked slowing of growth and even decreases in many of these
compounds as a result of implementation of the Protocol (WMO, 1998). Figure
1.5 shows the temporal change of ozone and surface UV radiation (at 45° N and
45° S) computed in correspondence to the halocarbon loading of the
atmosphere. This calculation assumes that changes in UV radiation are due
solely to ozone changes, which in turn are assumed to respond only to
atmospheric halocarbon loading. The quantitative relation between ozone and
halocarbon changes is based on the measured changes in both quantities
through the 1980s (Daniel et al., 1996). The future scenarios shown in the figure
are based on current control measures (Montreal 1997 Amendments), with
scenario A1 accounting for the fact that production of some ozone-depleting
29
substances is currently already below the allowed maximum, while under
scenario A3 production is at the maximum allowed level. In either case the UV
radiation is expected to return to normal (pre-1980) levels by the middle of the
next century. Scenario A2 shows the ozone/UV recovery if there is no emission
after the year 2000; while this scenario is obviously unrealistic, it illustrates the
natural time scale for the removal of the halocarbons already present in the
atmosphere, and is therefore a fundamental limit to the rate of recovery.
Given the numerous uncertainties listed above, it is unlikely that future UV
radiation changes will follow precisely any scenario presented in Figure 1.5. Two
features of this figure are nonetheless noteworthy. First, the return to pre-ozone
depletion levels will take several decades even under the most optimistic
scenarios of compliance with international regulations of ozone-depleting
substances. Second, and perhaps most important, is to note that in the present
half-decade (1995-2000) ozone reductions are the largest since ozone
observations began. The observed slowing and even turnover of the rate of
growth of some atmospheric halocarbons is highly significant, but large
uncertainties, stemming from both future human activities and the imperfect
understanding of the complexity of the atmosphere, leave open the question of
the extent and timing of the return to natural levels of stratospheric ozone and
surface UV radiation.
Future UV Radiation Levels ;The prediction of future UV radiation levels must be considered according to the
time scales of interest. On short time scales, of order of a few days or a week,
UV radiation forecasts incur all of the difficulties of forecasting weather
(especially clouds); of estimating atmospheric profiles of ozone and other gases
and particles, some anthropogenic; and of accounting for a variety of possible
other local factors including surfaces (elevation, orientation, reflectivity). These
factors make accurate UV forecasts impractical beyond a few days. Next-day
forecasts based on meteorological analyses are now being made with some
success in a number of countries. In most cases, the results are disseminated to
the public, with UV radiation levels expressed as a dimensionless UV index.
International standardization was reached (WMO, 1994b; ICNIRP, 1995) on the
method of calculation of the index, which is defined as the UV irradiance, in units
of W m-2, weighted by the erythemal action spectrum of McKinlay and Diffey
(1987), then multiplied by 40. Using this scale, a UV index of 10 or more may be
considered "extreme".
Long-term UV predictions (years, decades, or longer) are exceedingly difficult
and uncertain, and therefore only appropriate in a statistical sense of averages,
variabilities, and broad geographical patterns. Even then, many assumptions
must be made not only about the future state of the ozone layer, but also about
possible long-term changes in clouds, tropospheric pollutants, and changes in
surface albedo. In considering future biological effects of UV changes, it is also
30
necessary to allow for uncertain long-term changes in ecosystem size and
composition and - specifically for humans - changes in behavior, migration and
demographics.
Predictions of future ozone amounts are in themselves also very difficult.
Natural perturbations such as major volcanic eruptions are unpredictable, though
their importance to stratospheric ozone was clearly demonstrated in the
aftermath of the 1991 Mt. Pinatubo eruption. Large uncertainties exist concerning
the interactions of stratospheric chemistry with expanding human activities, e.g.
the increasing emissions of so-called greenhouse gases and the associated
changes in global climate, the effluents from growing fleets of subsonic and
supersonic aircraft, and the changes in tropospheric air quality and self-cleaning
(oxidizing) capacity. Their interactions with stratospheric ozone are current
subjects of active research and are still not well quantified (WMO, 1998). A
recent study, for example, suggests that the recovery of the ozone layer may be
delayed significantly by interactions with increasing green-house gas
concentrations .
Model-Derived Surface UV Radiation;In view of the high spatial and temporal variability of
surface UV radiation, and the difficulty of maintaining calibration within networks
of instruments, it is unlikely that either a satisfactory global UV climatology or
representative long-term UV trends can be derived from ground-based
monitoring stations alone. Satellite-based observations of the atmosphere, on the
other hand, provide the spatial (global or nearly global) coverage required for
climatology development, as well as nearly continuous long-term monitoring. For
example, the development of a climatology of UV radiation incident on the
oceans will necessarily be based on such satellite-derived estimates. However,
the derivation of surface UV irradiance from satellite-based observations is
indirect, because satellite instruments see radiation reflected by the atmosphere
and surface of the Earth. The determination of radiation transmitted to the
surface requires the use of radiative transfer models to relate transmission,
reflection, and atmospheric absorption.
Figure below shows the changes in UV radiation (at
310 nm) reaching the surface, computed for clear skies using satellite-based
ozone measurements between 1979 and 1993. As expected from ozone trends
(WMO, 1998), UV trends are not significant in the tropics, but increase pole-ward
in both hemispheres. The largest changes (percentage and absolute) are seen in
the Southern Hemisphere polar regions, but significant inter-annual and shorter
variability should be noted at all latitudes, even after considering monthly and
zonal averages. Patterns of long-term changes differ also between hemispheres,
e.g. with largest changes occurring in the early 1980s at southern mid-latitudes,
while northern mid-latitudes show a more persistent long-term trend.
31
Figure : Changes in daily surface spectral irradiances at 310 nm, computed for cloudfree conditions from satellite-based ozone observations
Significant progress has been made in recent years, in utilizing satellite-based
measurements of cloud cover as well as atmospheric ozone, to derive estimates
of surface UV radiation levels (Eck et al., 1995; Herman et al., 1996; Meerkoetter
et al., 1997). Recent work also suggests that it may be possible to derive
tropospheric aerosol distributions from satellite-based observations (Herman et
al., 1997; Krotkov et al., 1997; Hsu et al., 1997). Figure shows the type of
coverage and geographical detail currently possible with the satellite-based
approach. Long-term trends in cloud cover have partly offset or augmented UV
trends resulting from ozone changes in some regions, but have been shown by
Herman et al. (1996) to have little effect on long term changes when averaged
over large geographical scales (zonal means). This type of analysis represents a
considerable improvement over earlier analyses of satellite data that considered
only ozone changes, with no consideration of clouds (e.g., Medtronic, 1992 Table
32
shows the trends in surface UV radiation (erythemal weighting) over 1979-1992,
derived from measurements of ozone and cloud reflectivity by the Total Ozone
Mapping Spectrometer (TOMS, version 7) aboard the Nimbus 7 satellite. Positive
trends are statistically significant at the two-standard deviation level over much of
the mid-latitudes of both hemispheres. Extension to more recent years is
complicated by the use of different instruments aboard different satellites, and
analysis is still underway (WMO, 1998).
The limitations of these satellite-derived surface UV estimates should be
recognized. The ozone and cloud determinations at any specific location are
based on a single satellite overpass per day, and are estimated for other times
by interpolation or, more simply, by assuming constancy over the specific day.
Therefore it is essential that comparisons be made between ground-based UV
monitoring and the satellite-derived UV levels, in order to have a more complete
assessment of the uncertainties inherent in this method. Preliminary results of
such comparisons are encouraging (e.g. Eck et al., 1995) but more groundbased validation is needed over longer periods of time and different geographical
locations. Even so, comparisons to ground-based UV observations will not be
able to account fully for some location-specific biases. For example, optical
instruments borne by satellites have difficulty seeing the lower atmosphere (esp.
in the presence of clouds) so local conditions (e.g. pollution) is not sampled
accurately. Additional local factors, such as surface reflections and elevation
gradients, are also problematic. Other promising approaches combine, as above,
satellite data with radioactive transfer calculations, but also include some groundbased observations by other instruments such as visible and total solar radiation
detectors which are more accurate and much more widely deployed than UV
detectors
Measurements of UV Radiation
I.
II.
III.
Ozone-Related UV Radiation Changes :Cloud-Related UV Radiation Changes ;Aerosol-Related UV Radiation Changes
The last decade has seen a great increase in the
number and general quality of solar UV measurements. Many new commercial
and research-grade UV detectors have been developed, calibration procedures
have been improved, and several national and international intercomparisons
have been carried out (e.g. McKenzie et al., 1993; Gardiner et al., 1993;
Seckmayer et al., 1994; Thompson et al., 1997; Kjeldstad et al., 1997; Webb,
1997; Leszczynski et al. 1998). Agreement among similarly calibrated spectroradiometers is typically 5% or better in the UV-A range, and 5-10% in the UV-B
range. Comparisons between different types of instruments (e.g. spectroradiometers, broad band meters, filter radiometers) are more difficult, because of
the need to put the different measured quantities on a similar basis, for example
33
through the use of model interpolations (e.g. Slaper et al., 1995; Bernhard et al.,
1996; Mayer and Seckmeyer, 1996; Booth, 1997).
Direct measurements of surface UV radiation confirm to
a large extent the theoretical expectations, if allowances are made for local
conditions (e.g. Booth and Madronich, 1994; Forster et al., 1995; Geogdzhaev et
al., 1996; Gardiner and Martin, 1997; Mayer et al., 1997; Pachart et al., 1997;
Pfister et al., 1997; Weihs and Webb, 1997). However the analysis,
interpretation, and utilization of the measurements still lag behind the growing
data archives. Some general patterns of temporal and geographical variations
are also being identified (e.g. Seckmeyer et al., 1995; Bais et al., 1997; Bodhaine
et al., 1997; Lu and Li, 1997; Orce et al., 1997; Qu et al., 1997; Sasaki et al.,
1997; Zerefos et al., 1997; Bigelow et al. 1998). For example, ground-based
measurements show that summertime erythemal UV irradiances in the Southern
Hemisphere exceed those at comparable latitudes of the Northern Hemisphere
by up to 40% (Seckmeyer et al., 1995), whereas corresponding satellite-based
estimates yield only 10 to 15% differences (WMO, 1998). Atmospheric pollution
may be a factor in this discrepancy between ground-based measurements and
satellite-derived estimates. UV-B measurements at more sites are required to
determine whether the larger observed differences are globally representative.
Ozone-Related UV Radiation Changes:The evidence is overwhelming that under cloud-free
skies UV-B radiation is controlled largely by ozone (Bais et al., 1993; Kerr and
McElroy, 1993; Booth and Madronich, 1994; Diaz et al., 1994; Frederick et al.,
1994; Bojkov et al., 1995; Huber et al., 1995; Mims et al., 1995; Varatsos and
Kondratyev, 1995; Björn and Holmgren, 1996; Hofmann et al., 1996; Bernhard et
al., 1997; Bodhaine et al., 1997; Chubarova and Nezval, 1997; Kirchoff et al.,
1997; Koskela et al. 1997; Mayer et al., 1997; Seckmeyer et al., 1997; Taalas et
al., 1997; and references therein). The response of UV-B radiation to ozone
changes is strongly dependent on wavelength because of the rapid increase of
the ozone absorption cross section toward shorter wavelengths, with greater
sensitivity at short wavelengths and low sun, where the slant ozone optical depth
is greater [see for example the review by Madronich et al. (1995), the more
recent measurements by Fioletov and Evans (1997), and references therein]. For
biologically weighted radiation, measurements under cloud-free skies also show
the theoretically expected dependence on ozone. Figure 1.2 shows the sensitivity
of erythemal (skin-reddening) UV radiation to the ozone column amount, as
measured at a number of different locations and for different solar zenith angles.
When expressed on a relative (percentage) basis, the increases in erythemal UV
radiation are seen to correlate closely with ozone reductions, whether the latter
stem from natural fluctuations and seasonal cycles, or from systematic long-term
depletion. The largest percent UV increases are associated with the largest
percent reductions in atmospheric ozone.
34
Current losses of stratospheric ozone are discussed in
the Scientific Assessment of Ozone – 1998 (WMO, 1998). Relative to the values
in the 1970s, these are estimated to be about 50% in the Antarctic spring (the
ozone hole), about 15% in the Arctic spring, about 6% at Northern Hemisphere
mid latitudes in winter/spring, about 3% at Northern Hemisphere mid latitudes in
summer/fall, and about 5% at Southern Hemisphere mid latitudes year-round.
The corresponding increases in erythemal UV radiation are estimated to be
130%, 22%, 7%, 4%, and 6%, respectively. No significant ozone trend has been
found in equatorial regions. The geographical extent and severity of the Antarctic
ozone hole have remained essentially unchanged since the early 1990s.
Relatively little change in the mid latitude ozone losses has been observed in the
last half-decade. High levels of UV-B radiation have been observed directly in
association with the Antarctic ozone hole (Frederick and Alberts, 1991; Booth et
al., 1994; Seckmeyer et al., 1995, Frederick et al., 1998), and on occasion the
measured DNA-damaging radiation at Palmer Station, Antarctica (64° S) has
been found to exceed maximum summer values at San Diego, USA (32° N)
(Booth et al., 1994). It should be noted that monitoring of UV-B irradiances in
Antarctica began only in 1989, well after the appearance of the ozone hole, so
that the UV-B levels in pre-ozone hole years can be only estimated.
The smaller increases of UV-B radiation at mid
latitudes, while expected, have not yet been detected unambiguously. The record
of mid-latitude UV-B measurements is not sufficient for the derivation of
statistically significant trends. Little or no reliable historical information on the
climatology of UV radiation is available from pre-ozone depletion days (e.g., pre1980). The few available long-term UV measurement records have been
hampered by the difficulty in maintaining stability of UV-measuring outdoor
instruments over periods of decades, and by changes in atmospheric turbidity
associated with local pollution. For example, measurements obtained with
Robertson-Berger meters over 1974-85 suggested a decrease in UV radiation at
14 US locations (Scotto et al., 1988); however a recent re-analysis of these data
has identified calibration shifts which, when removed, indicate that no significant
trend can be derived from the data record (Weatherhead et al., 1997).
Furthermore, increases in UV due to stratospheric ozone reductions may have
been masked in some urban areas experiencing increasing levels of local air
pollution (e.g. Garadzha and Nezval, 1987). Pronounced ozone losses have
occurred for shorter periods of time, e.g. in the few years after the 1991 eruption
of Mt. Pinatubo (Gleason et al., 1993) and over the Arctic during six of the past
nine winters (Müller et al., 1997; Rex et al., 1997; Stolarski, 1997), with
correspondingly higher measured UV-B radiation levels (e.g. Kerr and McElroy,
1993; Fioletov and Evans, 1997).
Tropospheric ozone is also an effective absorber of UV-B radiation (Brühl and
Crutzen, 1989). In urban and industrialized regions, tropospheric ozone is formed
by the photo-chemical reactions of some pollutants (nitrogen oxides and
hydrocarbons), while in remote regions it stems from both downward transport
35
from the stratosphere, and from in-situ photochemical production by both natural
and anthropogenic precursor compounds transported from source regions
(WMO, 1994a). Model-based estimates suggest that for industrialized regions of
the Northern Hemisphere, the increases in tropospheric ozone since preindustrial times may have reduced DNA-damaging UV radiation by 3-15% (Brühl
and Crutzen, 1989; Madronich et al., 1991; Frederick et al., 1993; Blumthaler et
al., 1997; Ma and Guicherit, 1997). Comparisons between spectral UV
measurements in Germany and New Zealand also suggest that the lower UV
radiation levels observed in Germany may be explained partly by higher
tropospheric ozone levels (Seckmeyer and McKenzie, 1992). Recent changes in
tropospheric ozone are estimated to be much smaller those since pre-industrial
days, with both positive and negative trends reported for different geographic
locations (WMO, 1994a, 1998). Their contributions to the trend in the total ozone
column are much smaller than those from changes in stratospheric ozone over
the same time period (e.g., 1980 to present). Other gases such as sulfur dioxide
(SO2) and nitrogen dioxide (NO2) can also reduce atmospheric UV transmission,
however significant effects are limited to some extremely polluted urban
environments.
Cloud-Related UV Radiation Changes:Clouds generally reduce surface UV irradiances,
although the magnitude of this effect is highly variable depending on cloud
amount and coverage, cloud cell morphology, particle size distributions and
phase (water droplets and ice crystals), and possible in-cloud absorbers (esp.
tropospheric ozone). It is useful to note that under some conditions, UV
irradiances can be higher than for clear sky, as for example when both direct
sunlight and light scattered by clouds (e.g. the sides of bright broken clouds)
reaches the observer (Nack and Green, 1974; Mims and Frederick, 1994).
Numerous statistical correlations between UV
transmission and cloud cover have been carried out (e.g. Paltridge and Barton,
1978; Cutchis, 1980; Josefsson, 1986; Ilyas, 1987; Ito, 1993; Björn and
Holmgren, 1996; Estupinian et al., 1996; Schafer et al., 1996; Gillotay et al.,
1997), but because of the high spatial and temporal variability of clouds, no
single value can be given for their effects on surface UV levels. For example,
analysis of the Robertson-Berger meter data record shows that monthly average
UV levels are reduced by 10-50 percent, depending on season and location in
the US (Frederick et al., 1989, 1993). An important aspect of clouds is that, by
introducing strong variability in the UV intensities reaching the Earth’s surface,
they complicate the detection of long-term trends (Frederick and Erlick, 1995;
Lubin and Jensen, 1995; Nunez et al., 1997). Cloud transmission depends
somewhat on wavelength. In the UV-A region, transmission increases slightly
toward shorter wavelengths due to increased multiple reflections between cloud
and the surrounding air molecules (Nack and Green 1974; Seckmeyer et al.,
1996; Chubarova et al., 1997). At shorter wavelengths, in the UV-B range, long
36
photon path lengths in clouds can increase absorption by tropospheric ozone,
resulting in a sharp decrease in effective transmission (Frederick and Lubin,
1988; Mayer et al., 1998).
Aerosol-Related UV Radiation Changes:Small particles suspended in air (aerosols) can have a
significant effect on the transmission of UV-B radiation to the surface. The
magnitude of the effect is highly variable, depending on the number of particles
and their physical and chemical make-up (e.g. sulfate haze, soot, dust, sea-salt
aerosols). Such particles are frequently found in the lowest part of the
troposphere (the boundary layer), and are often associated with pollution.
Estimated that anthropogenic sulfate aerosols (associated
primarily with fossil fuel combustion) have decreased surface UV-B irradiances
by 5-18% in industrialized regions of the Northern Hemisphere. Additional
evidence for the role of aerosols comes from simultaneous monitoring of UV
irradiances and atmospheric turbidity in relatively polluted environments
(Garadzha and Nezval, 1987; Varotsos et al., 1995; Estupinian et al., 1996;
Mims, 1997), from differences between locations in the Northern (more polluted)
and Southern (less polluted) hemispheres (Seckmeyer and McKenzie, 1992;
Seckmeyer et al., 1995), and from the increases in UV irradiances with
increasing surface elevation, in excess of those expected from pollution-free
conditions (Cabrera et al., 1995; Madronich et al., 1995; Piazena 1996;
Blumthaler et al., 1997). The measured effects on UV radiation are highly
variable and specific to the various locations (e.g.,Wenny et al., 1998).
An important consideration is whether the aerosol particles
are highly absorbing (e.g. soot) or simply scatter (re-direct) the incident radiation
(e.g. sulfate aerosols). All particles tend to reduce the UV irradiance (defined as
the radiation incident on a horizontal surface). However, scattering by nonabsorbing aerosols can actually increase the UV exposure on non-horizontal
surfaces due to the additional radiation incident from low angles (e.g. Blumthaler
et al. 1997; Dickerson et al., 1997; Loxsom and Kunkel, 1997). The net effects on
biota from such changes in direction of incidence are not well understood.
Stratospheric aerosols are usually too sparse to have any
effect on atmospheric UV transmission. An exception arises following a major
volcanic eruption, such as that of Mt. Pinatubo (Philippines) in June 1991 which
injected large amounts of ash and sulfur dioxide (SO 2) into the stratosphere. The
heavier ash sedimented out of the stratosphere relatively quickly and its optical
effects were of limited geographical extent. Gaseous SO 2, on the other hand,
was removed from the stratosphere mainly by chemical reactions to form H 2SO4
molecules, which then readily nucleated into sulfate aerosol particles. Higher
stratospheric sulfate aerosol loadings were observed for several years after the
eruption, during which time these particles were distributed on global scales.
37
Calculations indicate that the effects on biologically weighted UV irradiances
were quite small, of order of a few percent (Madronich et al., 1991; Vogelmann et
al., 1992; Tsitas and Yung, 1996), with even some possible enhancements at
very short wavelengths and low sun when aerosols scatter some photons directly
downward thus allowing a shorter crossing of the stratospheric ozone layer
(Michelangeli et al., 1992; Davies, 1993). Ground-based measurements of UV
irradiance after the Mt. Pinatubo eruption confirm the small decreases and also
show a strong increase in diffuse/direct radiation at all wavelengths, in good
agreement with theoretical models (Blumthaler and Ambach, 1994; Zeng et al.,
1994, Lantz et al., 1996). A less direct but more important UV-related
consequence of stratospheric aerosols is their effect on stratospheric ozone
itself. Significant destruction of stratospheric ozone by heterogeneous chemical
processes involving the aerosols was predicted (Hoffman and Solomon, 1989;
Brasseur et al., 1990) and observed for several years after the Mt. Pinatubo
eruption
Collaborative Global Government Efforts:As a result of the many concerns that a thinning ozone
layer poses to society and the environment, the U.S. government and many
international agencies have been relatively active in attempting to monitor,
regulate, and solve the problem. Perhaps the most well known acts to help
control the depletion of the ozone layer were the Montreal Protocol, and the
London Ozone amendment to the Montreal Protocol. On September 14, 1987,
delegates from 43 countries met to discuss threats of the thinning ozone layer.
After much discussion, the delegates agreed to halt production and consumption
of CFCs at 1986 levels by the year 1990. In addition, nations also agreed to
reduce CFCs 20 percent by January 1, 1994 and an additional 30 percent by
January 1, 1999 (Roan, 208-9). This was known as the Montreal Protocol.
Even though this protocol helped the state of the ozone layer, the results were
not significant enough. Thus, shortly after the implementation of the protocol, in
1990, it was amended. This amendment recruited more countries, bringing the
total number involved to almost 100. The new goals were to eliminate the use of
all CFCs by the year 2000, and to help set up a fund so that developing countries
may find alternates to using CFCs. The name of this amendment was the
London Ozone Agreement. Thus, many nations recognized the need for rapid
and dramatic action in fighting the war with CFC responsible ozone depletion.
38
10.Waste Regulation
Depleters:-
&
Trade
Control
of
Ozone
Under the terms of the Montreal Protocol developed
nations have ceased production of new CFCs, halons and other ozone depleting
chemicals. Trade controls on the supply of these substances have been put in
place to ensure compliance with the Protocol. Existing CFCs are re-used and
recycled where possible. Nevertheless, the increasing price of CFCs as a result
of the ban on new production has led to a wave of international smuggling.
Waste Regulation and Recycling:Usually, when ozone depleting substances are
discarded or removed from equipment during the course of maintenance they
become controlled waste. In Britain, the Environmental Protection Act (1990) has
ensured that waste chemicals which may contribute to stratospheric ozone
depletion are disposed of as carefully as possibly to avoid any release to the
atmosphere.The production and consumption of new halons (halocarbons
containing bromine) has already ceased under the terms of the Montreal
Protocol. However, whilst replacements have been developed these cannot be
used in existing systems, which can only be maintained with recycled halons
using surplus material from redundant installations. In the UK the Halon Users'
National Consortium (HUNC) is managing the installed banks of halons, acting
as a clearing house putting those who need to continue to use halons in contact
with those who do not. The Montreal Protocol and subsequent amendments have
demanded that existing CFCs should be recovered, recycled and re-used where
possible. Commercial users of refrigeration and air conditioning appliances can
contact the Refrigeration Industry Board to ensure that best industrial practice is
maintained during the disposal or re-use of CFCs. Domestic users of old
refrigerators can contact their local authority to find out if it operates a CFC
recovery and recycling scheme.
Trade Controls:The Montreal Protocol works through a system of trade
barriers controlling supply to the market of ozone depleting chemicals. Imports of
newly produced CFCs and halons by developed countries have already been
banned, as have imports and exports in carbon tetrachloride and 1,1,1
trichloroethane. Developing countries have been
Most ozone-depleting substances are banned or strictly
controlled ;Many substances other than chlorofluorocarbons are also ozonedepleting. Examples are carbon tetrachloride (used in dry cleaning), and methyl
39
bromide (used as an insecticide for soil fumigation). An Australian scientist
(Jonathan Banks) has been internationally recognised for his work in finding a
replacement for methyl bromide CFCs, previously used as refrigerants, foamblowing agents and propellants in spray cans, are now banned in Australia (and
many
other
countries).
Their
temporary
replacements,
the
hydrochlorofluorocarbons, are still slightly ozone-depleting, though not to the
same extent. HCFCs are also being phased out. An international agreement
called the Montreal Protocol limits the production and use of ozone-depleting
substances. A slowing down in the rate of ozone loss has been measured, and
the concentration of CFCs in the atmosphere is levelling off. But because of a
long lag time, ozone depletion will get worse at least until the year 2000 and the
ozone hole will continue for some decades after that.
11.Controversy regarding ozone science and policy:There is no controversy or debate regarding ozone
depletion. There is a general consensus among most atmospheric physicists and
chemists that the scientific understanding has now reached a level where
countermeasures to control CFC emissions are justified, although the decision is
ultimately one for policy-makers. One atmospheric scientist, questions the
significance of the role that CFCs play in ozone depletion. Singer does not deny
that CFC's play some role, but believes that Despite this general consensus, the
science behind ozone depletion remains complex,. Although scientific
controversy exists, the possibility seems high that the depletion of the ozone
layer will prove detrimental if action is not taken. Regardless of the details of the
arguments, it is obvious that the depletion of the ozone layer is a serious problem
that poses many consequences to society. For example, research shows the
strong possibility of a number of health risks associated with increased UV-B
exposure as a direct result of the thinning ozone layer. These health risks
include skin cancer, immunes-suppression, cataracts, and ?snow blindness.?
Furthermore, the possibility that increased UV-B radiation results in lower crop
yields should provide a ?wake up? call to those who feel the thinning ozone layer
is not a problem. For if we are not able to breed UV-B resistant plants, the
world’s food supply would become dramatically decreased, resulting in higher
levels of famine and malnutrition. Studies from Antarctica tell society that
increased UV radiation can directly affect the food chain. Recall the decrease in
food supply as a result of reduced levels of phytoplankton in Antarctica. This
may seem like an isolated, non-significant, and remote problem; however, this
incident illustrates the dangers of reduced food supply and alteration of the food
chain as a result of the thinning ozone layer..
40
REFERENCES:-
1 . World Meteorological Organization in Scientific Assessment of Ozone
Depletion: 1994 Global Ozone Research and Monitoring Project WMO
Rep. 37 (WMO, Geneva, 1995).
2
Madronich, S. & de Gruijl, F. R. Nature 366, 23 (1993).
3
Congress of the United States. Office of Technology Assessment.
Catching
our
Breath:
Next
Steps
for
Reducing Urban Ozone. Washington: 1989.
4. Dotto, Lydia and Harold Schiff. The Ozone War. New York: Doubleday
and Company Inc., 1978.
5. Environmental Protection Agency.
6.
Environmental Protection Agency. "Ozone Depletion." Available:
http://www.epa.gov/docs/ozone/index.html
7.
Environmental Protection Agency. "The Science of Ozone
Depletion."
Available: http://www.epa.gov/ozone/science/
8.
Goddard
Distributed
Active
http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS
/ATM_CHEM/atmosphere_structure.html
Archive
Center
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