Atmospheric Chemistry and Physics

Abstract. The uptake kinetics of gaseous ClONO2 and BrONO2 on aqueous surfaces were measured, as a function of temperature and liquid composition (pure water and NaCl or NaBr containing solutions) using the droplet train tech-nique coupled to a mass spectrometer. The uptake kinetics are driven by the reactivity of these gases and, for both com-pounds, the uptake rates on pure water or on NaCl solutions (0.1 M) are comparable. The uptake coefficient γ of ClONO2 does not depend on the temperature while that of BrONO2 increases slightly when the temperature is raised from 272 to 280 K. For ClONO2 and BrONO2, the uptake rates in-crease on NaBr-doped droplets, enabling the estimation of the mass accommodation coefficient α. The corresponding values for α are 0.108±0.033 for ClONO2 and 0.063±0.021 for BrONO2 where the statistical errors correspond to ±2σ. The reactions of ClONO2 and BrONO2 on NaCl solutions lead respectively to the formation of Cl2 and BrCl. The up-take of ClONO2 on NaBr solutions generates BrCl as pri-mary product, which in turn can react with NaBr to produce Br2. As expected, the only product of BrONO2 reaction on NaBr solution is Br2.