The document discusses the ozone layer, its importance in absorbing UV radiation, and the layers of the Earth's atmosphere, including possible causes for ozone depletion. Primary culprits of this depletion are ozone-depleting substances such as chlorofluorocarbons (CFCs) which account for most of the damage. It also outlines efforts by UNEP OzonAction to assist nations in compliance with the Montreal Protocol to protect the ozone layer.

1. OZONE LAYER
IT’S DEPLETION AND IT’S EFFECT
BY: GROUP 4 (Roll. No.- 31 to 40)

2. The envelope of air or different types of gases surrounding the earth is known as atmosphere .
There are five distinct layers of atmosphere , they are as follows:-
1) TROPOSPHERE:-
This is the lowest atmospheric layer and is about 7miles(11km)thick ,the
troposphere is thinner at the poles and thicker at the equator . The
temperature decreases with altitude.
2) STRATOSPHERE:-
Above the troposphere is the stratosphere which extends to about 30-35 miles
about the Earth’s surface. The temperature rises within the stratosphere but
still remains well below freezing.
3) MESOSPHERE:-
The Mesosphere is above the stratosphere , here the temperature is very
rarefield , that is , thin , and the temperature is decreasing with altitude ,
about -130 Fahrenheit at the top.
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3. 4) THERMOSPHERE:-
The thermosphere rises several hundred miles above the earth’s surface. The
temperature is quite hot and can rise to as high as 3,600 degree Fahreneit.
5) EXOSPHERE:-
Extending from the top of the thermosphere to 6200 miles (10000 km) above the
earth is the exosphere . This layer has very low atmospheric molecules which can
escape into space.
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5. OZONE
LAYER  The ozone layer or ozone shield refers to
a region of Earth's stratosphere that
absorbs most of
the Sun's ultraviolet (UV) radiation.
 The ozone layer was discovered in 1913
by the French physicists Charles Fabry
and Henri Buisson.
 It contains high concentrations
of ozone (O3) relative to other parts of the
atmosphere, although still very small
relative to other gases in the stratosphere.
 The ozone layer contains less than 10
parts per million of ozone, while the
average ozone concentration in Earth's
atmosphere as a whole is only about 0.3
parts per million.
 The ozone layer is mainly found in the
lower portion of the stratosphere, from
approximately 20 to 30 kilometres (12 to
19 mi) above Earth, though the thickness
varies seasonally and geographically.
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6. 39
 The majority of tropospheric
ozone formation occurs when
nitrogen oxides (NOx), carbon
monoxide (CO) and volatile
organic compounds (VOCs), react
in the atmosphere in the presence
of sunlight. NOx, CO, and VOCs
are called ozone precursors.
 In the stratosphere, ozone is
produced by a two-step chemical
process.

7. *"ULTRA VIOLET" means "beyond violet". Violet being the colour of
the highest frequencies of visible light. Uv radiation was discovered
in 1801 when the German physicist " JOHANN WILHELM RITTER "
observed that invisible rays just beyond the violet end of the visible
spectrum darkened silver chloride.
*Ultraviolet (UV) light is an electro magnetic radiation with a wavelength from
400nm to 100nm, shorter than that of visible light but longer than X-rays. Uv
radiation is present in sunlight,and is produced by electric arcs. ultraviolet
radiations can cause chemical reactions and causes many substances to glow or
flouresce consequently. Suntan, freckling and sunburn are familiar effects of
over exposure along with higher risk of skin cancerabout 10% of sunlight is
UV and only about one- third of this penetrates the atmosphere to
reach the ground.Of this the solar UV energy that reaches the equator,
95% is UVA and 5% is UVB. No measurable UVC from solar radiation
reaches the earths surface, because ozone, molecular oxygen and
water
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8.  Destruction of the upper atmospheric layer of ozone gas, caused by substances
formed from breakdown of ozone depleting substances is called ozone depletion.
 Ozone is a triatomic form of oxygen (O3), found in the Earth's atmosphere. A
combination of low temperatures, elevated chlorine and bromine concentrations in the
upper stratosphere are responsible for the destruction of ozone. The production and
emission of chlorofluorocarbons (CFCs), is the leading cause of ozone layer depletion.
CFC's accounts for almost 80% of the total depletion of ozone.
 Other ozone-depleting substances (ODS), include hydrochlorofluorocarbons (HCFCs),
and volatile organic compounds (VOCs). These are often found in vehicle emissions,
byproducts of industrial processes, refrigerants, and aerosols. ODS are relatively
stable in the lower atmosphere of the Earth, but in the stratosphere, they are exposed
to ultraviolet radiation and thus, they break down to release a free chlorine atom.
 This free chlorine atom reacts with an ozone molecule (O3), and forms chlorine
monoxide (ClO), and a molecule of oxygen. Now, ClO reacts with an ozone molecule to
form a chlorine atom, and two molecules of oxygen. The free chlorine molecule again
reacts with ozone to form chlorine monoxide. The process continues, and this results
in the depletion of the ozone layer.
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9. Ozonaction Programme
 UNEP OzonAction assists developing
countries countries with economies in
transition to achieve and sustain their
compliance with the Montreal Protocol on
Substances that Deplete the Ozone Layer and
make informed decisions on alternative
technologies and ozone friendly policies.
 UNEP OzonAction has implemented over
1000 projects and services that have benefitted
to more than 100 developing countries. The
main objective is to the Montreal Protocol
whose annual per capita consumption and
production of ozone depleting substance is
less than 0.3 kg to comply with the control
measures of the protocol.
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• OzonAction is a branch of the United Nations Programme (UNEP) which has its
main office in Paris and is part of UNEP Division of Technology, Industry and
Economics created in 1991.

10.  The ozone-oxygen cycle is the process by which ozone is continually
regenerated in the Earth's stratosphere, all the while converting
ultraviolet radiation (UV) into heat. In 1930 Sydney Chapman
resolved the chemistry involved. The process is
commonlycalled the Chapman cycle by
atmospheric scientists.
 Most of the ozone production occurs in the tropical upper
stratosphere and mesosphere. The total mass of ozone produced per
day over the globe is about 400 million metric tons. The global mass
of ozone is relatively constant at about 3 billion metric tons,
meaning the Sun produces about 12% of the ozone layer each day
OZONE CYCLE
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11. Ozone Cycle
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12. 5 Ways to Protect Depletion of OZONE
 Limit private vehicle driving: by reducing the driving of vehicular emission
 Use eco-friendly houseold cleaning products: by using eco-friendly and
natural products which does not harm the environment.
 Avoid using pesticides: the best solution for this would be to try using
natural remidies,rather than heading out for pesticides.
 Developing stringent regulations for rocket launches: now –a-days no. of
rocket launches are pretty hgh which results in ozone depletion.Thus no. of
launches should be reduced or safe gases should be used for combustion.
 Banning the use of dangerous ‘nitrous oxide: nations around the globe
came together and formed ‘Montreal Protocol’ in the year 1989 with the
strong aim of stop usage of CFCs.
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