Characterization of Reactants, Reaction Mechanisms, and Reaction Products in Atmospheric Water Droplets: Fog, Cloud, Dew, and Rain Water Chemistry

摘要

Analyses of ground-based fogwater collected by inertial impaction in the Los Angeles basin, the San Gabriel Mountains, and the San Joaquin Valley revealed very high concentrations of NO3(-1), SO4(-2), NH4(+1), and other ions, often coupled with very high acidities. Fogs and stratus in the Los Angeles basin typically had pH values ranging from 2 to 4. Acidities were not as high in the San Joaquin Valley, mostly because of scavenging by the fogs of ammonia from agricultural sources. Deposition of fogwater was observed to be an important pollutant sink during stagnation episodes in the San Joaquin Valley, and may also be an important source of acid input to surfaces in some areas. Kinetic experiments showed that H2O2 is important in the oxidation of S(IV) to S(VI) at low pH. Metal-catalyzed autoxidation could also be an important source of sulfate. However, the extreme acidities observed in fogs (below pH 3) require condensation on preexistent acidic nuclei and scavenging of gaseous nitric acid. Stabilization of S(IV) in the fog was observed, and this was attributed to the formation of S(IV)-aldehyde adducts.