A study of sulfur dioxide oxidation pathways over a range of liquid water contents, pHs, and temperatures

摘要

We examine factors controlling the photochemical oxidation of SO_2 in tropos-pheric aerosols. Over a range of liquid water contents (3×10~(-4)g H_2O m~(-3) to 9 gH_2Om~(-3)) and pHs (0 to 8), we find that H_2O_2(aq) and O_3(aq) provide the major sinks for SO_2 in the aqueous phase when pH is below 5 and larger than 6, respectively. OH(aq) may be an important oxidant of SO_2 in the aqueous phase when pH is between 5 and 6 and H_2O_2 is depleted in an air parcel. When aerosols are present during noncloudy days in summer, the aqueous-phase oxidation of SO_2 is insignificant compared with the gas-phase oxidation of SO_2. We find however that the SO_2 oxidation in wet aerosols may be enhanced in winter or when the temperature is low (273K) and the relative humidity is high.