The exothermicity of reaction (5) has been estimated to be -3.7 kcal moU1 (e.g., Li and McKee, 1997).

Although the fate of the HOSOz adduct, and in particular the products of the H0S02-02 reaction, was controversial for a number of years, Stockwell and Calvert (1983) established that it must produce H02 since OH was regenerated in the presence of NO. This was subsequently confirmed by a number of researchers [e.g., see Meagher et al., 1984; Margitan, 1984; Martin et al., 1986; Gleason et al., 1987; Gleason and Howard, 1988; and Anderson et al., 1989] who measured the rate constant for reaction (5). This reaction is fast, with the current recommended rate constant being k5 = 4.3 X f0"13 cm3 molecule"1 s"1 at room temperature (Atkinson et al., 1997b). The lifetime of the H0S02 adduct is thus expected to be only 0.5 ¡xs at f atm in air.

While the S03 formed reacts rapidly with water, forming sulfuric acid,

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