Modeling studies of the effects of the heterogeneous reaction ClOOCl + HCl → Cl2 + HOOCl on stratospheric chlorine activation and ozone depletion

Abstract

The heterogeneous reaction ClOOCl + HCl → Cl2 + HOOCl was introduced into a chemical trajectory model of the stratosphere. Ten-day trajectories ending at ozonesonde stations at various northern latitudes were run to simulate the period January-March 1994. The reaction on sulfuric acid aerosol surfaces has a negligible effect on ozone chemistry if a sticking coefficient similar to that of ClONO2 + HCl is assumed. On polar stratospheric cloud (PSC) surfaces the chemical effects of the addition of this reaction depend on the fate of proposed product HOOCl: if this species photolyzes to produce either ClO + OH or Cl + HO2, then HCl is activated by the reaction with chlorine peroxide. This heterogeneous activation of chlorine by active chlorine can have a significant effect on Arctic ozone depletion rates in the days following an air parcel's encounter with PSC surfaces. The ozone depletion rate usually increased but in some cases decreased, depending on the extent of PSC processing and on the initial [HCl]/[ClONO2] ratio. Averaged over 3 months, the column ozone loss rates between 350 and 675 K were accelerated by as much as 35% for a set of 10-day trajectories ending at an Arctic station. If, on the other hand, HOOCl decomposes at the surface into HCl and O2, the net effect of these reactions is to convert ClOOCl into Cl2. These species are functionally equivalent, and such a conversion does not perturb the model chemistry. Copyright 1997 by the American Geophysical Union.