U.S. Dept. of Commerce / NOAA / OAR / PMEL / Publications
The cycling of sulfur through the troposphere plays an important role in atmospheric acid-base chemistry and in the formation and growth of aerosol particles. During the past century the natural biogeochemical sulfur cycle has been seriously perturbed over many areas of the globe, resulting in highly acidic precipitation and a dramatic increase in aerosol particle populations. The significance of these anthropogenic sulfur emissions, as well as the climatic importance of the natural atmospheric sulfur cycle, are difficult to assess without first quantifying the sulfur emissions from natural sources. Attempts to estimate natural sulfur emissions have been fraught with both a paucity of data and high natural variability.
The increased awareness of the environmental consequences of acidic precipitation has resulted in many recent measurements of both the sources of sulfur to the atmosphere and the processes involved in the cycling of sulfur through the atmosphere. These additional data permit us to re-assess earlier global natural sulfur emission estimates (Andreae, 1986) and to further refine these estimates on regional scales. These regional emission estimates are vital to our understanding of sulfur cycling because the atmospheric lifetime of most sulfur species is on the order of days (Summers and Fricke, 1989). Hence, global or even hemispherical sulfur budgets can obscure the climatic and environmental significance of the atmospheric sulfur cycle. There are, for example, vast regions over the remote oceans where natural sulfur emissions account for essentially all the atmospheric non-sea-salt (NSS) sulfate (Savoie and Prospero, 1989). On the other hand, the dominance of anthropogenic over natural sulfur emissions in the northeastern United States is underemphasized if one considers that globally, natural and anthropogenic sulfur emissions are of the same order of magnitude.
In this review, we combine the data from recent studies to calculate natural sulfur emissions on global, hemispherical, and regional scales. Included in these calculations are estimates of the uncertainties and natural variability.
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