On the kinetics and mechanism of oxidation of aquated sulfur dioxide by ozone

Abstract

Kinetic data obtained from a number of different investigators on the reaction of S(IV) with ozone in aqueous solution have been analyzed in terms of a single self-consistent rate expression. The rate expression that most appropriately fits all kinetic observations treated in this study is: −d[S(IV)]/dt = (k_0α_0 + k_1α_1 + k_2α_2)[S(IV)][O_3] where α_0, α_1, and α_2 denote the fraction of S(IV) in the form of SO_2·H_2O, HSO^−_3 and SO^(2−)_3, respectively. This kinetic expression is similar in form to the empirical rate laws reported by Erickson et al. (1977, Atmospheric Environment 11, 813–817) and Hoigne et al. (1985, Water Res. 19, 993–1004). The recommended values for k_0, k_1 and k_2 are (2.4 ± 1.1) × 10^4 M^(−1) s^(−1), (3.7 ± 0.7) × 10^5 M^(−1) s^(−1), and (1.5 ± 0.6) × 10^9 M^(−1) s^(−1), respectively. The activation energies that are recommended for k_1 and k_2 are taken from Erickson et al. (1977) as 46.0 kJ mol^(−1) and 43.9 kJ mol^(−1), respectively. The reaction proceeds via three independent pathways that involve a nucleophilic attack on ozone by SO^(2−)_3, HO-SO−_2, and SO_2·H_2O. Rate laws and kinetic data of five investigators are compared for an open cloud water system with a liquid water content of 0.2 g m^(−3).

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