10 What happens to organic chlorine in the stratosphere?
Description
This article is from the Ozone Depletion: Stratospheric Chlorine and Bromine FAQ, by Robert Parson rparson@spot.colorado.edu with numerous contributions by others.
10 What happens to organic chlorine in the stratosphere?
The organic chlorine compounds are dissociated by UV radiation
having wavelengths near 230 nm. Since these wavelengths are also
absorbed by oxygen and ozone, the organic compounds have to rise
high in the stratosphere in order for this photolysis to take
place. The initial (or, as chemists say, "nascent") products are
a free chlorine atom and an organic radical, for example:
CFCl3 + hv -> CFCl2 + Cl
The chlorine atom can react with methane to give HCl and a methyl
radical:
Cl + CH4 -> HCl + CH3
Alternatively, it can react with ozone to give ClO:
Cl + O3 -> ClO + O2
which can go on to react with O to release Cl again, closing
a catalytic cycle:
ClO + O -> Cl + O2
or can react with nitrogen dioxide to form the metastable compound
chlorine nitrate:
ClO + NO2 -> ClONO2.
(There are other pathways, but these are the most important.)
The other nascent product (CFCl2 in the above example) undergoes
a complicated sequence of reactions that also eventually leads to
HCl and ClONO2. Most of the inorganic chlorine in the stratosphere
therefore resides in one of these two "reservoirs". The immediate
cause of the Antarctic ozone hole is an unusual sequence of
reactions, catalyzed by polar stratospheric clouds, that "empty"
these reservoirs and produce high concentrations of ozone-destroying
Cl and ClO radicals. [Wayne] [Rowland 1989, 1991]
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