Rate constants for some oxidations of S(IV) by radicals in aqueous solutions

Rate constants were measured for several radical reactions important in the autoxidation of S(IV) in atmospheric droplets. For the reactions of the hydroxyl radical with sulfite and bisulfite, the rate constants were found to be 5.2 × 10¹⁰ and 4.5 × 10⁹ M⁻¹ s⁻¹, respectively. For the reaction of the dichloride radical anion with bisulfite, a rate constant of 3.4 × 10⁸M⁻¹s⁻¹ was obtained. The peroxysulfate radical was found to react with sulfite with a rate constant of 1.3 × 10⁷M⁻¹s⁻¹, but only an upper limit of 3×10⁵ could be derived for its reaction with bisulfite. In some cases, the rate constants are significantly different from those used previously in atmospheric models. The use of these results in a simple model suggests that secondary radical-radical reactions may be of considerable importance in the mechanism of sulfite autoxidation in the atmosphere.