Sulfur flux from anthropogenic sources

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. 

Table 10-17 includes a global atmospheric sulfur budget based on the emission estimates discussed in this chapter and the flux diagrams shown in Figs. 10-8 and 10-9. The marine budget of 36 Tg S/yr supplied by the biosphere must be augmented by about 6.8 Tg S/yr from anthropogenic sources. In addition, about one-half of the sulfur from volcanic emissions... 

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 ... 

Table 6.4.5 presents fluxes of sulfur compounds in the atmosphere as summarised by Friend (1973). Since the yearly inputs from anthropogenic and natural sources are known to be about two orders of magnitude larger than the atmospheric concentration, removal processes must delicately balance the injections. 

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