Sulfur compounds, global natural flux

The global natural flux of sulfur compounds to the atmosphere has recently been estimated to be about 2.5 Tmol yr1 (1) which is comparable to the emissions of sulfur dioxide (SO2) from anthropogenic sources (2). A substantial amount of the natural sulfur contribution (0.5-1.2 Tmol yr1) is attributed to the emission of dimethylsulfide (DMS) from the world s oceans to the atmosphere (3.4). One of the major uncertainties in this estimate is due to a scarcity of DMS and other sulfur data from the Southern Hemisphere, particularly the Southern Ocean region between about 40°S and the Antarctic continent, which represents about one fifth of the total world ocean area. 

Any improvement of the global model of the biosphere can only be achieved by extending our knowledge of the biogeochemical cycles involved in it. The need to parameterize a unit describing sulfur fluxes in natural systems is dictated by the dependence of biotic processes on the content of sulfur in biospheric compartments. The available data on the supplies and fluxes of sulfur compounds in the atmosphere, soils, vegetation cover, and hydrosphere, enable formulation of mathematical relationships to describe the global sulfur cycle. 

The sixth, seventh, and eighth sections of this volume deal with the atmospheric cycling of biogenic sulfur compounds. This aspect of the sulfur cycle has received a great deal of attention in recent years because of its obvious relationship to the add rain problem and the discovery that natural marine sources constitute a major portion of the total global atmospheric sulfur burden. The chapters in these sections focus on three aspects of this cycle field measurements and techniques used to establish the distributions and fluxes, experimental studies of reaction mechanisms and rates, and numerical simulations of the atmospheric sulfur cycle. Two chapters address the chemical processes involving cloud... 

On a global scale, natural emissions of reduced sulfur compounds account for about 50% of the total sulfur flux into the atmosphere (1-3). Hence, it is important to understand the natural sulfur cycle in order to establish a "base line" for assessing the significance of anthropogenic perturbations (primarily SO2 emissions). Dimethylsul-fide (DMS) is the predominant reduced sulfur compound entering the atmosphere from the oceans (4-9), and DMS oxidation represents a major global source of S(VI). The atmospheric oxidation of DMS can be initiated by reaction with either OH or NO3. In marine environments, however, NO3 levels are typically very low and DMS is destroyed primarily by OH ... 

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