Role of ozone in environment – Ozone layer – Ozone depleting gases – Green House Effect – Radioactive effects of Greenhouse gases – The Hydrological cycle – Green House Gases and Global Warming – Carbon Cycle. Ozone is a naturally occurring molecule made up of three oxygen atoms. It has the chemical formula O3. The word ‘ozone’ is derived from the Greek word óζειν which means “to smell”. Its strong smell allows scientists to detect it in low amounts. Ozone is found in different levels of the earth’s atmosphere. About 90% of ozone in the atmosphere is concentrated between 15 and 30 kilometres above the earth's surface (stratospheric ozone). At this level it provides a protective shield from the sun, we think of this as good ozone. It is also found at ground level in lower concentrations (tropospheric ozone). Here ozone is a pollutant that is a key part of smog over cities and we think of it as bad ozone. Atmospheric data demonstrates that ozone depleting substances are destroying ozone in the stratosphere and thinning the earth’s ozone layer. Ozone depleting substances are chemicals that include - chlorofluorocarbons (CFCs); nontoxic, nonflammable chemicals containing atoms of carbon, chlorine, and fluorine. halons, group of organohalogen compounds containing bromine and fluorine and one or two carbons.  carbon tetrachloride (CCl4), methyl chloroform (CH3CCl3), Hydro-bromo-fluoro-carbons (HBFCs), Hydro-chloro-fluoro-carbons (HCFCs),  methyl bromide (CH3Br) and bromochloromethane (CH2BrCl). They deplete the ozone layer by releasing chlorine and bromine atoms into the stratosphere, which destroy ozone molecules. These and other ozone depleting substances also contribute, to varying extents, to global warming

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Geethanjali College of Engineering and Technology
Cheeryala(V)
Keesara(M), Medchal Dist.
Telangana, INDIA
Pin Code-501301.
GLOBAL WARMING AND CLIMATE CHANGE

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UNIT I: Earth’s Climate System:
Role of ozone in environment –
Ozone layer –
Ozone depleting gases –
Green House Effect –
Radioactive effects of Greenhouse gases –
The Hydrological cycle –
Green House Gases and Global Warming –
Carbon Cycle.

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 Ozone is a naturally occurring molecule made up of three oxygen
atoms. It has the chemical formula O3.
 The word ‘ozone’ is derived from the Greek word óζειν which means
“to smell”. Its strong smell allows scientists to detect it in low amounts.
 Ozone is found in different levels of the earth’s atmosphere.
 About 90% of ozone in the atmosphere is concentrated between 15 and
30 kilometres above the earth's surface (stratospheric ozone).
 At this level it provides a protective shield from the sun, we think of
this as good ozone.
 It is also found at ground level in lower concentrations (tropospheric
ozone).
 Here ozone is a pollutant that is a key part of smog over cities and we
think of it as bad ozone.
What is ozone?

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Source- https://ozone.unep.org/one-gas-two-very-different-impacts-people-and-environment

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Ozone layer

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Ozone layer
 Ozone is a naturally
occurring molecule. An
ozone molecule is made up
of three oxygen atoms. It
has the chemical formula
O3.
 The ozone layer is one
layer of the stratosphere,
the second layer of the
Earth’s atmosphere.

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 The ozone layer is the common term for the high concentration of ozone that is
found in the stratosphere around 15–30km above the earth’s surface.
 Ozone is very rare in our atmosphere, averaging about three molecules of ozone
for every 10 million air molecules.
 The ozone layer effectively blocks almost all solar radiation of wavelengths less
than 290 nano-metres from reaching Earth’s surface, including certain types
of ultraviolet (UV) and other forms of radiation that could injure or kill most
living things
 It covers the entire planet and protects life on earth by absorbing harmful
ultraviolet-B (UV-B) radiation from the sun.
 Prolonged exposure to UV-B radiation is linked to skin cancer, genetic damage
and immune system suppression in humans and animals, and lower yielding
agricultural crops.
 The ozone layer is a thin part of the Earth's atmosphere that absorbs almost all of the
sun's harmful ultraviolet light.
 The ozone layer was discovered in 1913 by the French physicists Charles Fabry
and Henri Buisson.
What is the ozone layer?

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 Chemicals containing chlorine and bromine atoms are released to the
atmosphere through human activities.
 These chemicals combine with certain weather conditions to cause
reactions in the ozone layer, leading to ozone molecules being destroyed.
 Depletion of the ozone layer occurs globally, however, the severe
depletion of the ozone layer over the Antarctic is often referred to as
the 'ozone hole'.
 Increased depletion has recently started occurring over the Arctic as well.
What is the ozone hole?

10. The Antarctic
Ozone Hole

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 Atmospheric data demonstrates that ozone depleting substances are
destroying ozone in the stratosphere and thinning the earth’s ozone layer.
 Ozone depleting substances are chemicals that include -
1. chlorofluorocarbons (CFCs); nontoxic, nonflammable chemicals
containing atoms of carbon, chlorine, and fluorine.
2. halons, group of organohalogen compounds containing bromine and
fluorine and one or two carbons.
3. carbon tetrachloride (CCl4),
4. methyl chloroform (CH3CCl3),
5. Hydro-bromo-fluoro-carbons (HBFCs),
6. Hydro-chloro-fluoro-carbons (HCFCs),
7. methyl bromide (CH3Br) and
8. bromochloromethane (CH2BrCl).
 They deplete the ozone layer by releasing chlorine and bromine atoms
into the stratosphere, which destroy ozone molecules.
 These and other ozone depleting substances also contribute, to varying
extents, to global warming.
What is damaging the ozone layer?

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When was the depletion of the ozone layer discovered?
In 1974, chemists Mario Molina and Frank Sherwood
Rowland discovered a link between CFCs and the breakdown of
ozone in the stratosphere.
In 1985, geophysicist Joe Farman, along with meteorologists
Brian G Gardiner and Jon Shanklin published findings of
abnormally low ozone concentrations above the Antarctic, which
galvanized world-wide action.
In 1995, Mario Molina, Frank Sherwood Rowland and Paul
Crutzen, also an atmospheric chemist, were jointly awarded the
Nobel Prize in Chemistry "for their work in atmospheric
chemistry, particularly concerning the formation and
decomposition of ozone"

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 The ozone layer is depleted in two ways.
 Firstly, the ozone layer in the mid-latitude (e.g. over Australia) is
thinned, leading to more UV radiation reaching the earth.
 Data collected in the upper atmosphere have shown that there has
been a general thinning of the ozone layer over most of the globe.
 This includes a five to nine per cent depletion over Australia since
the 1960s, which has increased the risk that Australians already face
from over-exposure to UV radiation resulting from our outdoor lifestyle.
 Secondly, the ozone layer over the Antarctic, and to a lesser extent
the Arctic, is dramatically thinned in spring, leading to an 'ozone hole'.
 The Montreal Protocol on Substances that Deplete the Ozone Layer
came into effect in 1987.
 It sets binding obligations for countries to phase out production of
all the major ozone depleting substances.
 Data shows that stratospheric concentrations of ozone depleting
substances are declining.
 As a result of international action, the ozone layer is expected to
recover to pre-1980 levels over the mid-latitudes by 2050 and over the
polar regions by 2065.

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Uses of ozone depleting substances
 CFCs and HCFCs in refrigerators and air conditioners,
 HCFCs and halons in fire extinguishers,
 CFCs and HCFCs in foam,
 CFCs and HCFCs as aerosol propellants, and
 methyl bromide for fumigation of soil, structures and
goods to be imported or exported.

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Ozone depleting potential
 The Dobson Unit is the most common unit for measuring ozone concentration.
 One Dobson Unit is the number of molecules of ozone that would be required
to create a layer of pure ozone 0.01 millimeters thick at a temperature of 0
degrees Celsius and a pressure of 1 atmosphere (the air pressure at the
surface of the Earth).
 Expressed another way, a column of air with an ozone concentration of 1
Dobson Unit would contain about 2.69x1016ozone molecules for every
square centimeter of area at the base of the column.
 Over the Earth’s surface, the ozone layer’s average thickness is about 300
Dobson Units or a layer that is 3 millimeters thick.
 Ozone depleting potential is a measure of how much damage a chemical can
cause to the ozone layer compared with a similar mass of tri-chloro-fluoro-
methane (CFC-11).
 CFC-11, with an ozone depleting potential of 1.0, is used as the base figure for
measuring ozone depleting potential.
 The higher the number, the more damage a chemical can cause to the ozone
layer.
 Bromo-tri-fluoro-methane (halon-1301) has an ozone depleting potential of
10.0.

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1. 1974: Chemists in the USA discover the link between CFCs
and the breakdown of ozone in the stratosphere
2. 1985: British scientists publish results of abnormally low
ozone concentrations above the Antarctic
3. 1985: Vienna Convention for the Protection of the Ozone
Layer agreed.
4. 1987: Montreal Protocol on Substances that Deplete the
Ozone Layer agreed.
5. 1989: Ozone Protection and Synthetic Greenhouse Gas
Management Act commenced in Australia.
6. 1991: Phase out of CFCs (chlorofluorocarbons) begins
7. 1996: Phase out of HCFCs (hydrochlorofluorocarbons)
begins
Timeline

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