Atmospheric cycle of sulfur

On the basis of the foregoing discussion and further considerations the schematic atmospheric sulfur budget represented in Fig. 19 is proposed. The terms in the cycle were determined as follows. We accepted the figures of Friend (1973)for the strength of anthropogenic sources and for the sulfur production rate by volcanos (65 x 1061 yr 1 and 2 x 1061 yr respectively). On the other hand, we assumed, in accordance 

The wash-out of reduced sulfur compounds was neglected owing to the small solubility in water of these species. Furthermore it was assumed that the dry deposition of reduced compounds is negligible as compared to the strength of chemical sinks. Thus, Judeikis and Wren (1977) demonstrated by laboratory studies that the dry deposition velocity of DMS and H2S on selected soil samples ranges from 0.015 to 0.28 cm s 1. They mention, however, that these values are likely to be upper limits due to a possible reversible physical adsorption. 

For completeness the stratospheric inventory is also plotted in Fig. 19. The value of stratospheric sulfur burden is based on data for 1971-1973 as reported by Karol (1977). The term representing the sedimentation of sulfate particles from the stratosphere to the troposphere is estimated by assuming a 1 year stratospheric residence time (Junge, 1963). Moreover, the arrow going from the tropospheric-reduced S reservoir to the S04—S one in the stratosphere represents the possibility, proposed by Crutzen (1976), that COS may be a source of stratospheric S02. 

It follows from data given in Fig. 19 that the overall residence time of sulfur compounds in the atmosphere is 

We have to emphasize here that the majority of the sulfate-sulfur in the tropospheric reservoir in not sea salt. Friend (1973) estimated that the atmospheric sea-salt burden is around 0.1 x 106 t. By subtracting this value from the sulfate-sulfur loading given in Fig. 19 and considering only the strength of chemical sources (62 x 106 t yr 1), a residence time of more than 4 days is obtained for the excess sulfate. 

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Current research on the atmospheric cycling of sulfur compounds involves the experimental determination of reaction rates and pathways (see Plane review, this volume) and the field measurement of ambient concentrations of oceanic emissions and their oxidation products. Photochemical models of tropospheric chemistry can predict the lifetime of DMS and H2S in marine air however there is considerable uncertainty in both the concentrations and perhaps in the identity of the oxidants involved. The ability of such models to simulate observed variations in ambient concentrations of sulfur gases is thus a valuable test of our assumptions regarding the rates and mechanisms of sulfur cycling through the marine atmosphere. 

The atmospheric cycles of sulfur and nitrogen include the following components (a) emission of the compounds from the earth s surface into the atmosphere (b) transport and transformation of these compounds in the atmosphere (c) and wet and dry removal of the compounds from the atmosphere. The relationship between emissions levels and air and precipitation quality is a physical fact if the time and space boundaries are defined appropriately. For example, if the global emissions of sulfur increase, the average air quality for sulfur for the globe will decrease. This section will examine annual average values for source emissions estimates and for precipitation quality, for the northeastern United States for the mid-1950 s versus the late 1970 s. 

Reproduced with permission from R. J. Charlson, W. L. Chameides, and D. Kley (1985). The transformations of sulfur and nitrogen in the remote atmosphere. In "The Biogeochemical Cycling of Sulfur and Nitrogen in the Remote Atmosphere" (J. N. Galloway, R. J. Charlson, M. O. Andreae and H. Rodhe, eds), pp. 67-80, D. Reidel Publishing Company, Dordrecht.)... 

Comparison of Figs 13-6a and 13-6b clearly demonstrates the degree to which human activity has modified the cycle of sulfur, largely via an atmospheric pathway. The influence of this perturbation can be inferred, and in some cases measured, in reservoirs that are very distant from industrial activity. Ivanov (1983) estimates that the flux of sulfur down the Earth s rivers to the ocean has roughly doubled due to human activity. Included in Table 13-2 and Fig. 13-6 are fluxes to the hydrosphere and lithosphere, which leads us to these other important parts of the sulfur cycle. 

Increasing concentration of GHG in the atmosphere will lead to climate change and the most probable scenarios are related to sea level rise. According to these scenarios the mangrove ecosystems of the South East Asia and Thailand coast, in particular, will change many features, especially those connected with the biogeochemical cycle of sulfur. 

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... 

This global cycling of sulfur is closely linked to other geochemical cycles as well. In particular, it is tied to the abundance of atmospheric oxygen. 

The evolution of global cycling of sulfur as exemplified by Equations (19) and (20) above is closely tied to the evolution of atmospheric oxygen. Thus, sulfur geochemistry, particularly sulfur isotope data, has proved to be an important probe into the overall evolution of the Earth atmosphere system (Canfield et al., 2000 Canfield and Raiswell, 1999 Canfield and Teske, 1996 Knoll et al., 1998 Lyons et al., in press Schidlowski, 1979 Schidlowski et al., 1983). 

There will be changes in the future. Human emissions of sulfur dioxide to the atmosphere are likely to reach a maximum in the early twenty-first century. The biogeochemical cycle of sulfur seems set to undergo further change, so our retained interest is bound to unlock more of its secrets. 

In comparison to other spheres, the sulfur content of the atmosphere is small, about 1.8 Tg compared with 1.3 X 10 Tg for hydrosphere (Table 6.4.1). However, in terms of the global cycle of sulfur, the atmosphere plays a complex and critical role (Fig. 6.4.1). The residence time for sulfur in the atmosphere is considered to be a few days with wide variations dependent upon meteorological and other factors (Kellogg et al., 1972). This contrasts with the case of the lithosphere, for example, which although by far the largest sulfur reservoir, has a turnover time in the order of millions of years (Holser and Kaplan, 1966). The atmosphere is also the recipient of the majority of anthropogenic sulfur. 

The remainder of this chapter, which discusses the cycling of sulfur, is divided into an atmospheric part and an oceanic/solid earth part. The amount of sulfur in the atmosphere at any given time is small, even though the fluxes are large, because the lifetime of most sulfur compounds in air is relatively short (e.g. days). Sulfur in the ocean as SOj" is cycled much more slowly, and the primary interactions in that cycle are with the solid earth. 

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