AIR OXIDATION OF S(IV) IN-CLOUD WATER SAMPLES

Aerobic oxidation of S(IV) was investigated in cloud-water samples col lected at Great Dun Fell, U.K., as part of a wider project into cloud- water chemistry. The rate was found to be first-order in S(IV) concent ration, and the reaction rate constant, k(S(IV)), was found to vary fr om 10(-5) to 10(-3) s(-1). The rate constant was highly correlated wit h H+ concentration (pH 3.5 to 6.5) and Fe concentration (<0.02 to 3x10 (-6) mol dm(-3)). The aerobic oxidation of S(IV) does not contribute s ignificantly to SO2 oxidation in clouds at Great Dun Fell, however, th e reaction may be of consequence in clouds and fogs at polluted or urb an sites with elevated trace metal concentrations. Also, this reaction may be responsible for the oxidation of S(IV) in cloudwater samples d uring storage.