Uptake study of ClONO₂ and BrONO₂ by Halide containing droplets

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 technique coupled to a mass spectrometer. The uptake kinetics are driven by the reactivity of these gases and, for both compounds, the uptake rates on pure water or on NaCl solutions (0.1 M) are comparable. The uptake coefficient gamma 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 increase on NaBr-doped droplets, enabling the estimation of the mass accommodation coefficient alpha. The corresponding values for alpha are 0.108+/-0.033 for ClONO2 and 0.063+/-0.021 for BrONO2 where the statistical errors correspond to +/-2sigma. The reactions of ClONO2 and BrONO2 on NaCl solutions lead respectively to the formation of Cl-2 and BrCl. The uptake of ClONO2 on NaBr solutions generates BrCl as primary product, which in turn can react with NaBr to produce Br-2. As expected, the only product of BrONO2 reaction on NaBr solution is Br-2.