Measurements of the oxidation rate of sulfur (IV) by ozone in aqueous solution and their relevance to SO 2 conversion in nonurban tropospheric clouds

Abstract

An experimental survey of the rate of oxidation of sulfur (IV) by ozone in aqueous solution at 25 C in the pH range 3.1 to 6.2 has been conducted using stopped-flow spectrophotometry. The rates obtained are faster than those reported by Penkett et al. ( Atmospheric Environment (1979) 13, 123–137), but are in good agreement with an extension of the rates reported by Erickson et al. ( Atmospheric Environment (1977) 11, 813–817). Comparison of the present data with reported rates of oxidation of sulfur (IV) by H 2O 2 in aqueous solution at typical pH levels encountered in non-urban tropospheric cloud water, and at representative concentrations of O 3 and H 2O 2, indicates the potential importance of O 3 as a contributor to the oxidative conversion of SO 2 to sulfate in clouds. However, several orders of magnitude extrapolation in O 3 concentration are required in applying the present results to the environment, and verification by an experimental technique employing more representative O 3 concentrations is desirable.