Dimethyl sulfide mixing ratios

A widespread marine source of S02 is required to explain these observations. In Section 10.2 it was shown that the oceans release hydrogen sulfide and dimethyl sulfide, and that both are rapidly oxidized in the atmosphere by reaction with OH radicals. The processes convert hydrogen sulfide fully to S02, whereas dimethyl sulfide yields primarily methanesulfonic acid, and S02 accounts for only 25% of all products. Let us see whether the oxidation of these compounds suffices to explain the S02 mixing ratios observed in marine air. For this purpose we assume steady-state conditions and use the lifetimes for H2S and DMS given in Table 10-2. The mixing ratio for S02 at the ocean surface then is... 

According to Table 10-1 the mixing ratios for marine H2S are in the range 7-14 pptv, and those for dimethyl sulfide range from 5 to 60pptv. If the lifetime for S02 is about 4 days, one obtains... 

Fig. 10-9. Flux diagram for sulfur in the unperturbed marine atmosphere. Fluxes are given in units of p.gS/m2day. Numbers in boxes indicate column densities in units of p.gS/m2. DMS, Dimethyl sulfide MSA, methane sulfonic acid (associated with the aerosol). The mixing ratio of S02 is 60 ng S/m3, independent of altitude. The mixing ratio of SOis 280 ng S/m3 in the boundary layer and 80 ng S/m3 in the free troposphere. Contrary to the model of Kritz (1982), the fluxes are confined to the boundary layer. There exists no significant net flux into or out of the free troposphere. The dry deposition velocity for S02 is 5mm/s.

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