Heterogeneous photochemical sources of atomic Cl in the troposphere

The reaction of N2O5 with wet NaCl aerosol is observed to produce ClNO2 at high yields. The sticking coefficient of N2O5 on NaCl aerosol is determined in a smog chamber at 292 K, and the rate constant for the consecutive chemical reaction leading to formation of ClNO2 is determined at various relative humidities between 71 and 92 per cent. A preliminary evaluation of the experiments yields a sticking coefficient of 0.03, similar to that reported for pure water droplets. At the deliquescence point of NaCl, appr. 50 per cent of the collisions lead to the formation of ClNO2. This portion decreases slightly with increasing humidity. The process is expected to be and efficient sink of N2O5 in the troposphere. Model calculations indicate a significant contribution of atomic Cl to global marine tropospheric chemistry at higher latitudes of the northern hemisphere. Phosgene, chloroacetone, and 1,1-dichloroacetone are observed as products from a heterogeneous chlorination in the aerosol smog ch amber.