OZONE DEPLECTION

SUJEET S. TAMBE
OZONE DEPLECTION
INTRODUCTION
Ozone is both beneficial harmful to us. Near the ground, ozone forming as a
result of chemical reactions involving traffic pollution and sunlight may cause a number
of respiratory problems, particularly for young children. However, high up in the
atmosphere in a region known as the stratosphere, ozone filters out incoming radiation
from the Sun in the cell-damaging ultraviolet (UV) part of the spectrum. Without this
ozone layer, life on earth would not have evolved in the way it has. Concentrations of
ozone in the stratosphere fluctuate naturally in response to variations in weather
conditions and amounts of energy being released from the Sun, and to major volcanic
eruptions. Nevertheless, during the 1970s it was realized that man-made emissions of
CFCs and other chemicals used in refrigeration, aerosols and cleansing agents may cause
a significant destruction of ozone in the stratosphere, thereby letting through more of the
harmful ultraviolet radiation.
Then in 1985 evidence of a large "ozone hole" was discovered above the
continent of Antarctica during the springtime. This has reappeared annually, generally
growing larger and deeper each year. More recently, fears have emerged about significant
ozone depletion over the Arctic, closer to the more populous regions of the Northern
Hemisphere. Protecting the ozone layer is essential. Ultraviolet radiation from the Sun
can cause a variety of health problems in humans, including skin cancers, eye cataracts
and a reduction in the body's immunity to disease. Furthermore, ultraviolet radiation can
be damaging to microscopic life in the surface oceans which forms the basis of the
world’s marine food chain, certain varieties of crops including rice and soya, and
polymers used in paints and clothing. A loss of ozone in the stratosphere may even affect
the global climate.

SUJEET S. TAMBE
The destruction of the ozone layer, which protects all living things from harmful
ultraviolet solar radiation, was one of the first, global environmental problems to be
understood by the general population and tackled by the international community.
The subsequent measures against the use of chlorofluorocarbons (CFCs), halons, and
other ozone depleting chemicals made their production and emission drop significantly.
As a result, the total concentration of chlorine in the lower atmosphere peaked in 1994.
The long life of those substances in the atmosphere means that full recovery of the ozone
layer is unlikely before 2050, however.
The remaining policy challenges for European countries are to tighten control
measures, to reduce the production and use of HCFCs and methyl bromide, to manage
banks of existing ozone-depleting substances, and to support developing countries in their
reduction of the use of ozone-depleting substances.
A GIANT UMBRELLA OVER THE EARTH-
You have probably heard
people talk about a "hole" in
our ozone layer. Damage to our
Earth's giant protective
umbrella is more severe in the
South Pole, but, even there, no
actual "hole" exists. And only a
slight thinning occurs over the
rest of the world. So no matter
where you stand, you won't
find a true "hole".
About 20 kilometers thick, this
giant umbrella is made up of a
layer of ozone gas. This gas is
found some 15 to 35 kilometers
above the Earth's surface in the
upper atmosphere or
"stratosphere".
CAUSES OF OZONE DEPLECTION

SUJEET S. TAMBE
Ozone depletion occurs when the natural balance between the production and
destruction of stratospheric ozone is tipped in favour of destruction. Although natural
phenomena can cause temporary ozone loss, chlorine and bromine released from man-
made compounds such as CFCs are now accepted as the main cause of this depletion. It
was first suggested by Drs. M. Molina and S. Rowland in 1974 that a man-made group of
compounds known as the chlorofluorocarbons (CFCs) were likely to be the main source
of ozone depletion. However, this idea was not taken seriously until the discovery of the
ozone hole over Antarctica in 1985 by the British Antarctic Survey.
Chlorofluorocarbons are not "washed" back to Earth by rain or destroyed in
reactions with other chemicals. They simply do not break down in the lower atmosphere
and they can remain in the atmosphere from 20 to 120 years or more. As a consequence
of their relative stability, CFCs are instead transported into the stratosphere where they
are eventually broken down by ultraviolet (UV) rays from the Sun, releasing free
chlorine. The chlorine becomes actively involved in the process of destruction of ozone.
The net result is that two molecules of ozone are replaced by three of molecular oxygen,
leaving the chlorine free to repeat the process:
Cl + O3 ClO + O2
ClO + O Cl + O2
Ozone is converted to oxygen, leaving the chlorine atom free to repeat the process
up to 100,000 times, resulting in a reduced level of ozone. Bromine compounds, or
halons, can also destroy stratospheric ozone. Compounds containing chlorine and
bromine from man-made compounds are known as industrial halocarbons.
Emissions of CFCs have accounted for roughly 80% of total stratospheric ozone
depletion. Thankfully, the developed world has phased out the use of CFCs in response to
international agreements to protect the ozone layer. However, because CFCs remain in
the atmosphere so long, the ozone layer will not fully repair itself until at least the middle
of the 21st
century. Naturally occurring chlorine has the same effect on the ozone layer,
but has a shorter life span in the atmosphere.

SUJEET S. TAMBE
ENVIRONMENTAL EFFECTS
OF OZONE DEPLETION-
Table of Contents-
1. Ozone and UV Changes
2. Health Effects
3. Effects on Aquatic Ecosystems
4. Effects on Biogeochemical Cycles
Ozone and UV Changes-
Reductions in stratospheric ozone are continuing, both in the Antarctic with the
re-appearance of the ozone "hole" each spring, and at other locations and times in both
hemispheres. High latitudes of the northern hemisphere have experienced very low ozone
in the last two winters, apparently due to record-low temperatures in the lower
stratosphere, which favor the formation of polar stratospheric clouds and thereby the
activation of ozone-destroying chlorine. Mid-latitude ozone levels in both hemispheres
remain significantly lower than during the 1980s. Record low ozone recently observed at
some lower latitude locations (e.g., Mauna Loa) during 1994/95 was probably mainly due
to stratospheric circulation changes rather than to chemical causes. Re-analysis of ozone
measurements from the Total Ozone.
Mapping Spectrometer (TOMS) aboard the Nimbus-7 satellite has been carried
out recently. However, detailed comparisons between the re-analyzed data and the earlier
(version 6) TOMS data, the other satellite data (e.g., SBUV and SBUV/2), and the
ground-based ozone measurements (Dobson instruments) are yet to be published.
Substantial progress has been made in the estimation of global surface UV levels
through the assimilation of satellite-derived data into radioactive transfer models. In
contrast to earlier models, which accounted only for variations in ozone, these new
techniques appear promising for including also the effects of clouds and possibly aerosols
on UV transmission. One study, based on 1979-1992 ozone and cloud reflectivity data
from TOMS (version 7), gives erythemal UV trends that are smaller (by 10-50%,
depending on latitude) than the cloud-free trends previously estimated from TOMS
version 6, SBUV and SBUV/2 ozone data.
However, clouds had only a minor impact on the trends of the new study, and the
discrepancies appear to result from the lower ozone trends estimated from the new
version 7 TOMS data.
The record of direct UV measurements is still too short for reliable estimation of
long-term trends. However, recent measurements at both polar and middle latitudes show
the expected relationship between episodic ozone decreases and UV increases. Surface

SUJEET S. TAMBE
UV-monitoring continues to expand, with international coordination under the auspices
of the World Meteorological Organization (WMO) and the Network for Detection of
Stratospheric Change (NDSC). Several international comparisons of monitoring
instruments have been carried out, and confirm earlier estimates of usual agreement at the
5% level in the UV-A and 10% in the UV-B.
Intercomparisons among UV radiation models, and between models and
measurements are also being carried out or planned.
The effects of clouds on atmospheric and surface radiation have received
considerable theoretical and observational attention in the last year. Topics of active
research have included the spectral dependence induced by clouds (showing more
effective transmission of UV-B than visible radiation), and the complex effects of non-
uniform and broken cloud fields.
Health Effects-
The principal impacts of UV on health are mediated through two organ systems,
the skin and the eyes, which receive all of the exposure. These systems are generally
either well adapted to (the skin) or well protected from (the eyes) such exposures;
humans benefit from UV exposures through the initiation of Vitamin D3 production, and
even detrimental effects such as DNA damage, are normally corrected by efficient repair
mechanisms.
Our average day-to-day exposure to UV is generally sufficient to ensure appropriate
levels of Vitamin D. There is some evidence in tissue culture that Vitamin D has
inhibitory effects on tumor cell growth. Such effects have been suggested as the
mechanism underlying an observed increase in breast and colon cancers at higher
latitudes (where solar exposures are less). This linkage is still conjectural, however. The
production of the biologically active vitamin is self-limiting so that excessive exposures
are not likely to be associated with any benefit.
New findings with regard to the molecular events underlying UV-induced no
melanoma skin cancer extend the earlier observations that these tumors often have
alterations (mutations) in a particular (p53) tumor suppressor gene that are typical of UV-
B radiation. The recent findings indicate that similar UV-B alterations in a second tumor
suppressor gene (ptc) are associated with spontaneous (non-hereditary) basal cell
carcinomas (BCC). These data provide the most direct evidence that UV-B radiation
contributes to the development of these skin tumors.
Additional studies on the involvement of p53 indicate that the frequency of such
typical UV-B alterations in the skin tumors may decrease with lower dose levels and
spectral shifts toward the long wave UV-A. An additional finding in UV-induced
carcinogenesis comes from recent epidemiologic studies, which indicate that BCC is not
principally related to cumulative UV dose, but as with melanoma, appears to be more
related to childhood and intermittent over-exposures.

SUJEET S. TAMBE
New epidemiologic studies on melanoma for the most part confirm earlier work.
Several studies have suggested that sunscreen use may not be protective for melanoma
and may even be associated with increased risk.
A possible explanation offered to explain these observations is that wearing
sunscreens, while reducing UV-B exposure, provides little protection from UV-A
exposures and that such exposures are important to melanoma risk. Although such an
interpretation is in line with the spectral response of melanoma induction in a fish model,
such epidemiologic findings may be biased by linkages among susceptibility, exposure
and sunscreen use. New work in the opossum model for melanoma has shown that short-
term neonatal exposures to broadband UV-B/UV-A radiation (of approximately a week)
result in highly aggressive (met static) melanomas.
It is now clear that there are at least three mechanisms by which UV-B exposures
may suppress cellular immunity: DNA damage, isomerization of urocanic acid and
through the active metabolite of vitamin D. Immune effects can occur both locally at the
skin and systemically throughout the body. The local effects have long been considered
important to the development of skin cancer, but there has been little evidence found with
regard to the importance of systemic effects. Recent observations of an increase in non-
Hodgkin's lymphoma with increasing solar radiation have led to the suggestion that UV-
B-induced systemic immunosuppressant contributes to cancer development in this
system. The implications of either local or systemic immune effects for human infectious
diseases are still unknown. Epidemiological studies are still required to explore these
issues.
There is very little new information on UV effects on the eye. A critical lack is an
action spectrum for eye effects associated with chronic exposures, e.g., cataract.
Effects on Aquatic Ecosystems-
In the recent past, scientific and public interest has focused on marine primary
producers and aquatic ecosystems, which resulted in a multitude of studies indicating
mostly detrimental effects of UV-B radiation on aquatic organisms. The interest has
expanded to include effects in individual species as well as specific responses and has
concentrated on ecologically significant groups and major biomass producers using
mesocosm studies, emphasizing species interactions. In addition, light penetration into
the water column was investigated by several research groups.
Macro algae and sea grasses are major biomass producers in aquatic ecosystems.
In contrast to phytoplankton most of these organisms are sessile and can thus not avoid
the exposure to solar radiation at their growth site. Recent investigations showed a
pronounced sensitivity to solar UV-B, and effects have been found throughout the top 10
- 15 m of the water column. Mechanisms of protection and repair are being investigated.
Controversy still exists regarding the interpretation of data on UV-B effects in
Antarctic phytoplankton. Estimates of the decreases in overall biomass productivity by

SUJEET S. TAMBE
different authors range from 0 - 12%. Most recently, shifts in phytoplankton community
structure have been demonstrated, which may have consequences for the food web.
Bacteria play a vital role in mineralization of organic matter and provide a tropic
link to higher organisms. Recently, the mechanism of nitrogen fixation by cyan bacteria
has been shown to be affected by UV-B stress. Wetlands constitute important ecosystems
both in the tropics and at temperate latitudes. In these areas cyan bacteria form major
constituents in microbial mats.
The organisms optimize their position in the community by vertical migration in
the mat which is controlled by both visible radiation and UV-B. Cyan bacteria are also
important in tropical and subtropical rice paddy fields where they contribute significantly
to the availability of nitrogen. Growth, development and several physiological responses
of these organisms are affected by solar UV.
Dissolved organic carbon (DOC) and particulate organic carbon (POC) are
degradation products of living organisms. These substances are of importance in the
cycling of carbon in aquatic ecosystems. UV-B radiation has been found to break down
high molecular weight substances and make them available to bacterial degradation. In
addition, DOC is responsible for short wavelength absorption in the water column.
Especially in coastal areas and freshwater ecosystems, penetration of solar radiation is
limited by high concentrations of dissolved and particulate matter. On the other hand,
climate warming and acidification result in faster degradation of these substances and
thus enhance the penetration of UV radiation into the water column.
UV effects on aquatic animals have found increased interest. In addition to effects
on larval stages in amphibian, sea urchins were found to be affected by solar UV-B
radiation despite the fact that they have partial protection from mycosporine amino acids,
which they take up with their food. Corals have been known to be directly affected by
solar UV; in addition, photosynthesis in their symbiotic algae is impaired, resulting in
reduced organic carbon supply.
All of the previous studies on UV penetration into the water column were based
on occasional measurements. This will be corrected by a recent project involving the
development of a monitoring system (ELDONET) for solar radiation in Europe using
three-channel dosimeters (UV-A, UV-B, PAR), which are being installed from Abisko
(North Sweden, 68° N, 19° E) to Tenerife (Canary Islands, 27° N, 17° W). Some of the
instruments will be installed in the water column (North Sea, Baltic Sea, Kattegat, East
and Western Mediterranean, North Atlantic), establishing the first network of underwater
dosimeters for continuous monitoring.
Effects on Biogeochemical Cycles-

SUJEET S. TAMBE
Terrestrial studies are continuing to examine the influence of enhanced UV-B
radiation on microbial decomposition of plant litter to carbon dioxide and nutrients.
Additional studies have confirmed that litter from plants grown under enhanced UV-B is
enriched in lignin and decomposed to CO2 more slowly by soil microorganisms.
The fate and transport of trifluoroacetate (TFA), a persistent substance derived
from the oxidation of certain CFC replacements (HFC-123, HFC-124, HFC-134a), was
investigated in a temperate forest of North America. The study indicates that the added
TFA was retained in vegetation and soil, especially in the case of wetlands with organic
soils. In addition, biological accumulation was observed as was a lack of microbial
consumption.
Studies of photo degradation of dissolved organic carbon (DOC) by UV radiation
are continuing and expanding. Several studies published over the past year have provided
additional evidence that exposure to UV radiation enhances the degradation of DOC to
CO2 and ammonium. In addition, low- molecular-weight organic products are produced
and are readily assimilated by microorganisms.
Volatile compounds are produced by aquatic DOC photo degradation and
additional studies of the photo production of carbon monoxide have appeared. CO is an
important trace gas that strongly influences biogeochemical cycles through its effects on
chemical reactions in the atmosphere. Two new studies of marine CO photo production
have resulted in disparate estimates of global oceanic sea-to-air emissions. These two
global flux estimates are two orders of magnitude apart: 10-15 Tg CO year-1
and 1000 Tg
year-1
(1 Tg = 1012
g). Total annual emissions of CO from all sources, by comparison, are
about 2000-2500 Tg year-1
primarily from fossil fuel combustion and CH4 oxidation.
New modeling approaches are being developed to predict the interactions and
feedbacks between climate change and UV-B induced changes in marine biogeochemical
cycles. Important links exist between oceanic dimethylsulfide (DMS) production, sea-to-
air DMS flux and subsequent changes in the sulfate aerosol-related atmospheric radiation
balance. These alterations indicate possible consequences with regard to climate and
climate prediction, because DMS is an important source of cloud condensation nuclei
over parts of the ocean.
PRECAUTIONS-

SUJEET S. TAMBE
Can do to both protect the ozone layer. These include proper disposal of old
refrigerators, the use of halons-free fire extinguishers and the recycling of foam and other
non-disposable packaging. Finally, we should all be aware that whilst emissions of ozone
depletes are now being controlled, the ozone layer is not likely to fully repair itself for
several decades. Consequently, we should take precautions when exposing ourselves to
the Sun.
CONCLUSION-
Ozone is both beneficial and harmful to us. Ozone Deflection can cause a variety
of health problems in humans, including skin cancers, eye cataracts and a reduction in the
ability to fight off disease. Ozone forming as a result of chemical reactions involving
traffic pollution and sunlight may cause a number of respiratory problems, particularly
for young children Therefore Ozone Deflection is very big problem.
The ozone layer is not likely to fully repair itself for several decades.
Consequently, we should take precautions when exposing ourselves to the Sun.
The air pollution is main cause of Ozone Deflection. Therefore we can stop the
air pollution. We can stop the air pollution by minimum use of vehicles and the plantation
of trees.

OZONE DEPLECTION

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