Oxidation by Ozone in the Aqueous Phase

While the emphasis has been on oxidation of DMS and other reduced sulfur compounds in the gas phase, there is some indication that oxidation in the aqueous phase in clouds and fogs should also be considered. For example, Lee and Zhou (1994) have shown that DMS reacts with 03 in aqueous solutions quite rapidly, with a rate constant at 288 K of 4 X 108 L mol-1 s-1. They estimate that at 30 ppb 03, a level found globally, the lifetime for in-cloud oxidation of DMS is about 3 days, of the same order of magnitude as that for the gas-phase oxidation by OH (see Table 8.17). Given the moderately high solubility of not only DMS but other sulfur compounds as well (see Henry s law constants in Table 8.1), this is clearly an area that warrants further research. 

As seen from the data in Table 8.17, the OH reaction with CH3SSCH3 (DMDS) is almost two orders of magnitude faster than that with DMS. Because of its 

The reaction of OH with dimethyl disulfide proceeds primarily by addition to a sulfur atom. As discussed by Abbatt et al. (1992), although one would expect abstraction of an H atom from the CH3 group to occur as well at about the same rate as for DMS, such a channel is overwhelmed by the fast addition. 

The CH3S and CH3SOH then react in a manner analogous to the reactions discussed for the DMS oxidation, ultimately forming S02 and methanesulfonic acid (e.g., Hatakeyama and Akimoto, 1983 Barnes et al., 1994a). 

The mechanism of the N03 radical reaction with DMDS is complex. The rate constants for the N03 reaction with CH3SCH3, CH3SH, and CH3SSCH3 (Table 8.17) are similar and much larger than that for the reaction with H2S. This suggests that by analogy with the dimethyl sulfide reaction, the initial step is addition to a sulfur atom to form an adduct that then reacts further  

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