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Recent data suggest that due to the release
into the atmosphere of CFCs by human activities, the ozone hole can as large as
North America during a given astral spring. The CFCs are broken apart by UV
light--to form free radicals of chlorine--after they have diffused into the
upper stratosphere from the troposphere. This long term movement from the
troposphere to the stratosphere is possible for these chlorine containing
chemicals because of there long atmospheric lifetimes; however, this type of
movement is not important for more reactive species such as tropospheric ozone
because of their reactivity and therefore short atmospheric lifetime. In the
Antarctic stratosphere, the reaction that converts
reservoir species of chlorine into an active form--which destroys
ozone--takes place on the surface of particles in polar stratospheric clouds as
the temperature drops below about200K. This is possible because of the unique
isolation of the south polar vortex during the austral winter. The surfaces of
these (nitric acid/water) clouds act as catalysts for reactions that release
molecular chlorine which quickly photolyzes to chlorine's (radical) active
state. It is this radical which destroys ozone.
[Journal of Atmospheric Science;
v51; 2846-2866; 1994.] [New Scientist; v139; 18; 1993.] [Geotimes; v38; 7;
1993.] [Science News; v144; 232-235; 1993.]
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