THE POTENTIAL OF CIRRUS CLOUDS FOR HETEROGENEOUS CHLORINE ACTIVATION

The ER-2 data from ascents and descents through layers of cirrus cloud s are utilized to study the heterogeneous reactions of ClONO2 with H2O , of HOCl and ClONO2 with HCl, and their potential role for the activa tion of chlorine in the tropopause region, which could affect ozone th ere. Lacking measured data for the three chlorine containing molecules their abundances as a function of altitude have been calculated fr om a 2D model. The aerosol surface data measured by a Forward Scattering Spectrometer Probe (FSSP-300) on the ER-2 were corrected for the expe cted asphericity of cirrus cloud particles by means of a T-matrix meth od. The results indicate considerable potential of cirrus clouds for c hlorine activation. If ClONO2 and HCl are present in the tropopause re gion they are likely to be quickly converted to active chlorine by cir rus clouds.