The effects of coexisting NaSO on heterogeneous uptake of NO on CaCO particles at various RHs.

Atmospheric particles can undergo nucleation, coagulation, chemical-aging, dissolution-precipitation or other atmospheric processes, resulting in complex multicomponent aerosols. The coexisting species have potentially important consequences in the heterogeneous reactions of multicomponent aerosol particles with polluted gases, which are still poorly understood. The effect of coexisting NaSO on heterogeneous uptake of NO on CaCO particles is investigated in a broad RH range. The combination of DRIFTS, Raman, SEM and IC provides qualitative and quantitative information about the formation of nitrate and other surface species. Ca(NO) and NaNO are generated on mixed CaCO-NaSO particles under dry condition. Both the amount of NO formed and the NO formation rates for the mixtures can be predicted based on the linear addition of those for pure CaCO and NaSO particles under dry condition. The further reaction of Ca(NO) with NaSO could lead to the formation of crystal NaNO and CaSO·0.5HO at 30% RH. Coagulation between Ca and SO in surface adsorbed water is observed after part conversion of CaCO to Ca(NO), resulting in the formation of CaSO·2HO at 80% RH. The amount of NO formed on the mixtures is dramatically enhanced relative to the predictions at 30% and 80% RH. The findings presented here highlight the role of coexisting species in the heterogeneous reactions of trace gases with multicomponent aerosols due to the complexity of atmospheric particles.