REACTIVE UPTAKE OF CLONO2 ONTO SULFURIC-ACID DUE TO REACTION WITH HCLAND H2O

The uptake of ClONO2 onto sulfuric acid solutions and HCl-doped sulfur ic acid solutions has been measured over temperature and composition r anges relevant to the high-latitude lower stratosphere. The results re veal that the reaction of ClONO2 with HCl in/on sulfuric acid is an im portant source of active chlorine for the stratosphere. It is suggeste d that ClONO2 uptake due to reaction with HCl is dependent on both bul k and surface concentrations of HCl and that, for present levels of HC l in the stratosphere, the surface-dependent uptake could be a signifi cant contributor to the conversion of ClONO2 and HCl to Cl-2 at temper atures less than 195 K, if type I PSCs are not formed at their thresho ld temperatures. The hydrolysis of ClONO2 and the gamma for uptake in the absence of HCl have been shown to be dependent on the activity of water. The results suggest a larger reactive uptake at temperatures ne ar 200 K than has been used previously. The parameters obtained from t hese uptake measurements will lead to better representations of the Cl ONO2 + H2O and ClONO2 + HCl reactions in atmospheric models.