HETEROGENEOUS ATMOSPHERIC BROMINE CHEMISTRY

This paper considers the effect of heterogeneous bromine reactions on stratospheric photochemistry. We have considered reactions on both sul fate aerosols and on polar stratospheric clouds (PSCs), It is shown th at the hydrolysis of BrONO2 on sulfate aerosols enhances the HOBr conc entration, which in turn enhances the OH and HO2 concentrations, there by reducing the HCl lifetime and concentration. The hydrolysis of BrON O2 leads to a nighttime production of HOBr, making HOBr a major nightt ime bromine reservoir. The photolysis of HOBr gives a rapid increase i n the OH and HO2 concentration at dawn, as was recently observed by Sa lawitch et al. [1994]. The increase in the OH and HO2 concentration, a nd the decrease in the HCl concentration, leads to additional ozone de pletion at all latitudes and for all season. At temperatures below 210 K the bulk phase reaction of HOBr with HCl in sulfate aerosols become s important. The most important heterogeneous bromine reactions on pol ar stratospheric clouds are the mixed halogen reactions of HCl with HO Br and BrONO2 and of HBr with HOCl and ClONO2.