O

o ch3sch3

o ch3sch3 oh ch3sch2. 02J

no} no2^ ch3sch2o-fast J

0 xch3s>:+hcho ch3sch2o2no2-

ch3so o2

I 02

ch3sch3

ii j

0

II

ch3soh

+

dmso2

ch3»

"CH2S multi-steps >[OCS

"CH2S multi-steps >[OCS

FIGURE 6.19 Mechanism for OH reaction of dimethyl sulfide (DMS).

and a bimolecular reaction, with a fairly small activation energy:

Higher temperatures favor the decomposition step relative to the bimolecular reaction. This behavior is also consistent with a path from the DMS-OH adduct to MSA, as indicated by the dashed line in Figure 6.19.

An interesting finding with implications for the global sulfur cycle is that OCS is a minor product of the DMS-OH reaction, under NO^-free conditions, with a yield of 0.7% S (Barnes et al. 1996). Even at an OCS yield of only 0.7% of DMS oxidized, this path would represent a significant input to the global cycle of OCS, corresponding to an OCS source strength in the range of 0.10-0.2B Tg yr"1 of OCS.

The DMS-N03 reaction proceeds initially by an H-atom abstraction (Jensen et al. 1992)

CH3SCH3 + N03 —>■ CH3SCH2- + HN03 and therefore leads directly to CH3S.

Because all the steps of the DMS oxidation chemistry by OH and N03 are not completely understood, some investigators have used measured marine DMS and S02 concentrations as a means of inferring important aspects of the mechanism such as the yield of S02 from DMS oxidation [e.g., see Yvon et al. (1996) and Yvon and Saltzman (1996)]. The latter investigators estimated S02 yields from DMS oxidation to range from 27 to 54% for conditions in the tropical Pacific marine boundary layer.

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