Active chlorine release on H2SO4 aerosol particles via the reaction of HOCl and HCl in solution is discussed. Based on current laboratory data, the process is shown to have an appreciable rate at temperatures below about 195 K, when the aerosol particle become sufficiently dilute to allow both HCl dissolution and fast ClONO2 hydrolysis. Evolution of part-per-billon concentrations of Cl2 could be significant in cases in which volcanically enhanced aerosol remains liquid until the frost point (≈190 K) as observed on several occasions in the Arctic stratosphere. ¿American Geophysical Union 1994