Chlorine chemistry in the Antarctic stratosphere: Impact of OClO and Cl2 O2 and implications for observations

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Abstract
Theories have been proposed to relate the reduction of O3 during antarctic spring to catalytic cycles involving chlorine and bromine species. A necessary condition for any chlorine‐catalyzed scheme is that a large fraction of the chlorine must be in the form of ClO in the lower stratosphere. It has been suggested that these high levels of ClO could be maintained by fast heterogeneous reactions, whose rates are not known at present. Model calculations based on the above mechanisms predict considerable amounts of OClO and Cl2O2, particularly during the night. We present results of calculations of the diurnal variations of ClO, OClO, and Cl2O2 during antarctic spring, for different cases. Results from our calculations suggest that coincident measurements of the total column abundance and diurnal variation of ClO and OClO may help constrain key aspects of the proposed chemical mechanisms. Removal of O3 by the catalytic cycle involving Cl2O2 could be as important as that involving BrO for present levels of chlorine, provided that Cl2O2 photolyzes rapidly to yield Cl and ClO2. We show that there is no synergy between these two cycles, since they both compete for the available ClO.