Sulfur dioxide oxidation in laboratory clouds

Abstract

SO 2 oxidation in the presence of NH 3 was studied in a mixing-type continuous-flow cloud chamber. NaCl and soot particles (∼5–15 μ m −3) were used as cloud condensation nuclei. Cloud liquid water content was varied between 0.2 and 3 g m −3. SO 2 and NH 3 concentrations were 0.6 and 1.1 ppm, respectively. The contact time between the SO 2 and the cloud drops was varied from 8 s to 3 min. Up to 80% of the input SO 2 can be oxidized within short contact times in the presence of NH 3 and when the water is in the condensed cloud-drop phase. Negligible sulfate formation was observed in the absence of the liquid phase regardless of the presence or absence of NH 3. No significant dependence of the oxidation on the cloud condensation nuclei type nor the contact time was found. This in-cloud SO 2 oxidation is much faster than predicted by S(IV) oxidation by molecular oxygen measured in bulk solutions.