S IV Oxidation by the OH Radical

APPENDIX 7.2 ADDITIONAL AQUEOUS-PHASE SULFUR CHEMISTRY 7.A.1 S(IV) Oxidation by the OH Radical 

Free radicals, such as OH and H02, can be scavenged heterogeneously from the gas phase by cloud droplets or produced in the aqueous phase. More than 30 aqueous-phase reactions involving OH and H02 have been proposed (Graedel and Weschler 1981 Chameides and Davis 1982 Graedel and Goldberg 1983 Schwartz 1984 Jacob 1986 Pandis and Seinfeld 1989a). 

Chameides and Davis (1982) first proposed that the reaction of aqueous hydroxyl radicals with HS03 and SO3 may represent a significant pathway for the conversion of S(IV) to sulfate in cloudwater. The reaction chain is initiated by the attack of OH on HS03 and SO3- to form the persulfite radical anion, SOJ (Huie and Neta 1987)  

These reactions are elementary and have rate constants, at 298 K, k7.A1 = 4.5 x 

S03 then reacts rapidly with dissolved oxygen to produce the peroxymonosulfate radical, S05  

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