Heterogeneous Photochemical Sources of Atomic Cl in the Troposphere

Abstract

Abstract The reaction of N 2 O 5 with wet NaCl aerosol is observed to produce ClNO 2 at high yields. The sticking coefficient of N 2 O 5 on NaCl aerosol is determined in a smog chamber (in an inserted teflon bag) at 292 K, and the rate constant for the consecutive chemical reaction leading to formation of ClNO 2 is determined at various relative humidities between 71 and 92%. A preliminary evaluation of the experiments yields a sticking coefficient of 0.03( −0,01 +0,02 ), similar to that reported for pure water droplets. At the deliquescence point of NaCl, ∼ 50% of the collisions lead to the formation of ClNO 2 . This portion decreases slightly with increasing humidity (i.e. liquid water content of the NaCl aerosol). The process is expected to be an efficient sink of N 2 O 5 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 chamber.