AUTOCATALYTIC RELEASE OF BROMINE FROM ARCTIC SNOW PACK DURING POLAR SUNRISE

Measurements and modeling studies strongly suggest that spring time de pletion of ozone in the Arctic planetary boundary layer (PBL) is due t o catalytic destruction by bromine atoms. However, the source of the b romine is uncertain. In this note, we propose that the source of the b romine at polar sunrise is the snow pack on the ice covering Arctic oc ean and that it is released auto-catalytically, stimulated by a bromin e seed from one of the brominated organic compounds, such as CHBr3, by photolysis. In this manner similar to 100 pptv of bromine can be tran sferred to the atmosphere where it can reside in the gas phase or, by scavenging, be partitioned in the aerosol or ice crystal phase. Moreov er, it appears that heterogeneous recycling of bromine may be a proces s that self-terminates as ozone depletes to low levels. We also have i ncluded chlorine chemistry in the model in order to simulate inferred levels of chlorine atoms. This is important as it results in the produ ction of HCHO which acts to convert post ozone depletion active bromin e into HBr which is then returned to the snow pack or scavenged by aer osols or ice crystals.