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TitleOzone Depletion Biology Project
TagsAtmosphere Of Earth Ultraviolet Chlorofluorocarbon Ozone Depletion Stratosphere
File Size410.9 KB
Total Pages29
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Page 14

made compounds such as CFCs are now accepted as the main
cause of this depletion [10]. 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 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.
A. Chlorofluorocarbons
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
(dichloro-tetrfluoroethane-C2F4Cl2), and CFC-115
(chloropentafluoroethane - C2F5Cl).CFCs are widely used as

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