ABSTRACT

The oxidation rate of sulfite was determined in its dilute solution. The reaction is substantially of the first order and the rate is much accelerated by the presence of small amounts of heavy metals such as iron, copper and manganese. The half-life time of sulfite in the natural rain water is more than a few hours. The observed concentration of sulfite in rain water is nil or much smaller than that of sulfate. Thus, the anthropogenic sulfur is removed from the atmosphere after the oxidation to sulfate in air or in cloud droplets. The residence time of aerosol sulfur of anthropogenic origin and the mean-life time of sulfur dioxide for the oxidation are estimated to be 10 days and 30 hrs, respectively, from the concentrations of sulfate and ²¹⁰Pb in precipitation. It is inferred from the experiments and the observations that excess sulfate in meteoric precipitation is essentially of anthropogenic origin.