THE CHLORINE BUDGET OF THE LOWER POLAR STRATOSPHERE - UPPER LIMITS ONCLO, AND IMPLICATIONS OF NEW CL2O2 PHOTOLYSIS CROSS-SECTIONS

Chlorine catalytic chemistry, which destroys ozone while cycling chlor ine between Cl, ClO, and Cl2O2, is the primary cause of the springtime Antarctic ozone hole. We have calculated the concentrations of Cl2O2 which are in equilibrium with midday ground-based, aircraft, and satel lite observations of ClO in the Antarctic spring lower stratosphere. T wo significant conclusions are presented here: (1) Using the JPL 94 re commended rates and photolysis cross sections, more than similar to 2. 0 ppbv ClO in the polar lower stratosphere causes inferred total activ e chlorine to exceed the total chlorine budget. This limit is smaller than some reported ClO measurements. (2) Using smaller cross sections recently measured by Huder and DeMore [1995], the amount of Cl2O2 in m idday equilibrium with measured ClO is approximately doubled. Activate d chlorine inferred from many measurements then exceeds total chlorine in the lower stratosphere, suggesting these cross sections may be too small.