Reduced sulfur cycling in the marine boundary layer

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Eric S. Saltzman - Committee Chair


This study is a field and laboratory investigation of the cycling of biogenic sulfur gases over the oceans. The sources of atmospheric reduced sulfur compounds are characterized over the remote oceans. Possible conversion pathways and turnover times are assessed in both clean marine air and more polluted air. The role of biogenic emissions in the global sulfur cycle is assessed. Implications for the origin of non-sea-salt sulfate over the oceans are discussed.Field data from the remote marine atmosphere are reported in this study in reasonable agreement with previous work. Simultaneous measurements of dimethylsulfide (DMS) with hydrogen sulfide (H$\sb2$S) and carbon disulfide (CS$\sb2$) suggest that estimates of the contribution of the latter two compounds to the sulfur burden of the marine atmosphere may have been overestimated in the past.Measurements of DMS in the pollutant plume over the western Atlantic ocean show significant diurnal variation, in contrast to previous reports. This report can be explained largely through meteorological effects, but also indicate a higher DMS loss rate during the day than seen in more remote locations. This daytime loss rate is also higher than evident at night. These observations suggest that the presence of pollutants leads to enhanced daytime oxidation rather than enhanced nighttime oxidation, as previously suggested.Both the field data and the results of laboratory gas exchange experiments indicate that the flux of dimethylsulfide from the sea surface to the atmosphere is approximately a factor of two lower than previously believed. Using this lowered flux in models of sulfur cycling resolves many of the current inconsistencies in the literature concerning DMS levels and diurnal cycling. This lower flux suggests that biogenic sulfur plays only a minor role in the global sulfur cycle. DMS is observed to be the major component of the natural sulfur flux to the atmosphere. Oxidation of natural reduced sulfur gases is therefore only a minor source of sulfate in rainfall. It is suggested that alternative explanations are needed to explain the apparent magnitude of sulfate deposition over the remote oceans.


Biogeochemistry; Chemistry, Analytical

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