Sulfur Cycle

Among the general categories of tropospheric sulfur sources, anthropogenic sources have been quantified the most accurately. Research on fluxes of sulfur compounds from volcanic sources is now in progress. Natural sources of reduced sulfur compounds are highly variable in both space and time. Variables, such as soil temperature, hydrology (tidal and water table), and organic flux into the soil, all interact to determine microbial production and subsequent emissions of reduced sulfur compounds from anaerobic soils and sediments. Available information on sources of COS, CS2, DMS, and H2S to the troposphere in the following paragraphs are summarized; these are the major biogenic sulfur species with a clearly identified role in tropospheric chemistry. The oxidation of SO2 to H2SO4 can often have a significant impact on the acidity of precipitation. A schematic representation of some important transformations and sinks for selected sulfur species is illustrated.