Stratospheric Ozone Depletion by Chlorofluorocarbon
Abstract
Man-made chlorofluorocarbons (CFCs) such as CCl2F2 and CCl3F are inert
in the lower atmosphere and can survive for a hundred years or more
without reaction. The only important destruction process for CFCs is
ultraviolet photolysis in the stratosphere, with the release of atomic
chlorine. Chlorine atoms attack stratospheric ozone with the formation
of the free radical ClO which reacts further to regenerate atomic
chlorine. This chain reaction can cause the removal of 100000 molecules
of ozone per Cl atom, and coupled with the emission to the atmosphere of
one million tons of CFCs per year, produces ozone depletion on a
significant global scale. Under the special meteorological conditions of
the Antarctic winter stratosphere, chlorine and nitrogen chemistry occur
which permit massive ozone depletion in the lower stratosphere when
sunlight returns in the spring. Similar chemistry has also been found in
experiments carried out in the Arctic stratosphere. Analysis of
long-term records from ground stations has confirmed the loss of 2-3%
ozone since 1970 in the Northern Hemisphere between 30¡N and 64¡N,
with the heaviest losses in the winter. The Montreal Protocol of 1987
provides a framework for international control of emissions of CFCs, and
its 1990 modification calls for elimination of further production within
the next decade. Substitutes for the CFCs are now being developed
rapidly, with special attention to HCFCs (e.g. CHClF2) and HFCs (e.g.
CH2FCF3) whose primary removal occurs through oxidation in the lower
atmosphere.
Rowland, F. Sherwood, 1990: Stratospheric ozone depletion by
chlorofluorocarbons. Ambio 19, 281-292.
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