INTERACTIONS OF AEROSOLS (AMMONIUM-SULFATE, AMMONIUM-NITRATE AND AMMONIUM-CHLORIDE) AND OF GASES (HCL, HNO3) WITH FOGWATER

The concentrations of aerosols (NH4NO3, (NH4)2SO4 and NH4Cl) and of gases (HCl(g), HNO3(g), NH3(g) were determined by denuder methods under different conditions (in the absence of fog, before, during and after fog events). At this site situated in an urban region, high concentrations of the gaseous strong acids HCl(g) and HNO3(g) are observed. NH4Cl and NH4NO3 aerosols represent a major fraction of the Cl- and NO3- aerosols (<2.4 μm)collected by denuders. During a fog event, very high concentrations of SO42- were found in small aerosols, which are attributed to the aqueous phase oxidation of SO2 under the influence of high pH due to the presence of NH3. Differences in SO42- concentrations measured in aerosols (<2.4 μm) and in fog droplets were probably due to mass-transport limitations of the SO2 oxidation. Ammonium sulfate aerosols represent in some cases a significant fraction of the total S present (SO2(g) + SO42-. Soluble aerosols and gases contribute to the composition of fogwater and are released again after fog dissipation. © 1990.