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 What
is ozone layer destruction?
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 Advancing
destruction of the ozone layer
| The ozone layer, situated in the stratosphere
about 15 to 30 km above the earth's surface, plays the important
role of "space suit" that protects us living beings
by absorbing harmful ultraviolet radiation (UVB) from the sun.
The ozone layer is currently being destroyed by CFCs and other
substances, its depletion progressing globally except in the
tropical zone.
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The ozone layer is disappearing at a particularly
high rate in high-latitude areas.
In the Antarctic Circle, a large ozone hole has been observed
for eight consecutive years from 1989 through 1996.
NB: m atm-cm, milli-atmosphere centimeter indicates
total ozone amount, i.e., the amount of ozone contained in
a vertical air column in the atmosphere; 300 atm-cm has a
thickness of 3 mm when ozone in the air column is entirely
compressed at 0
and 1 atmospheric pressure. |
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Annual Change in Three Ozone Hole Factors
(Meteorological Agency: Ozone Layer Observation Report, 1996) |
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Impact
of ozone layer destruction
- Destruction of the ozone layer increases the amount of harmful
ultraviolet radiation (UVB), which in turn can result in increased
cases of skin cancer, and visual impediments such as cataract. It
can also hinder the growth of plants and negatively impact small
living organisms, such as zooplankton, phytoplankton, shrimp larvae
and the young of fish.
What
is CFC?
- CFC, chlorofluorocarbon, is the collective name for compounds
made of carbon, fluorine, chlorine and hydrogen. Because of their
stable, harmless and non-combustible properties, they are widely
used in everyday applications such as cleansing agents for electronic
components, coolants for air conditioners, foaming agents for the
manufacture of insulating materials and so on. CFC variations include
HCFC and HFC.
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CFC (Chlorofluorocarbon)
Because of CFC's strong ozone layer-destroying effect, its production
was totally banned at the end of 1995.
It is necessary to ensure proper handling of CFC in appliances currently
in use.
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HCFC (Hydrochlorofluorocarbon)
Although less powerful than CFC in destroying the ozone layer, HCFC
must be also contained.
Mechanism
of ozone layer destruction by CFCs
- Since CFCs are chemically stable, when released into the atmosphere
they pass through the troposphere at about 20 km altitude without
decomposing, reaching the stratosphere, where they are chemically
decomposed by short-wavelength ultraviolet rays, releasing chlorine
atoms. In a chain reaction, the chlorine atoms destroy the ozone
layer in the stratosphere.
Mechanism of Ozone Layer Destruction
by CFC in Stratosphere
Prediction
of future ozone layer destruction
- The 1994 general report of the scientific, environmental impact
and technological economic assessment panel of the UNEP predicted
that the amount of chlorine and bromine would peak in 1994 in the
troposphere, while in the stratosphere it would reach peak 3 - 5
years later and begin to decrease, provided that all the signatory
countries observe the revised Montreal Protocol of 1992.
From this, it is predicted that the global ozone decrease will continue
during the remaining years of the 20th century, but that if other
factors remain unchanged, the ozone layer will begin to be restored
in the early 21st century and the Antarctic ozone hole will disappear
around the year 2045.
Effective Straospheric Chlorine Concentration
(1994 UNEP report)
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