Sulfur cycle deposition

The harmful effects of air pollutants on human beings have been the major reason for efforts to understand and control their sources. During the past two decades, research on acidic deposition on water-based ecosystems has helped to reemphasize the importance of air pollutants in other receptors, such as soil-based ecosystems (1). When discussing the impact of air pollutants on ecosystems, the matter of scale becomes important. We will discuss three examples of elements which interact with air, water, and soil media on different geographic scales. These are the carbon cycle on a global scale, the sulfur cycle on a regional scale, and the fluoride cycle on a local scale. 

Fig. 4-13 Calculated and observed annual wet deposition of sulfur in mgS/m per year. (Reprinted from "Atmospheric Environment," Volume 30, Feichter, J., Kjellstrom, E., Rodhe, H., Dentener, F., Lelieveld, and Roelofs, G.-J., Simulation of the tropospheric sulfur cycle in a global climate model, pp. 1693-1707, Copyright 1996, with permission from Elsevier Science.)...

Figure 13-5 is the box model of the remote marine sulfur cycle that results from these assumptions. Many different data sets are displayed (and compared) as follows. Each box shows a measured concentration and an estimated residence time for a particular species. Fluxes adjoining a box are calculated from these two pieces of information using the simple formula, S-M/x. The flux of DMS out of the ocean surface and of nss-SOl back to the ocean surface are also quantities estimated from measurements. These are converted from surface to volume fluxes (i.e., from /ig S/(m h) to ng S/(m h)) by assuming the effective scale height of the atmosphere is 2.5 km (which corresponds to a reasonable thickness of the marine planetary boundary layer, within which most precipitation and sulfur cycling should take place). Finally, other data are used to estimate the factors for partitioning oxidized DMS between the MSA and SO2 boxes, for SO2 between dry deposition and oxidation to sulfate, and for nss-SO4 between wet and dry deposition. 

Truper H. G. (1982) Microbial process in the sulfur cycle through time. In Mineral Deposits and the Evolution of the Biosphere (eds. S. H. Holland and M. Schidlowski). Springer, Berlin, pp. 5-30. 

Fig. 13-5 The sulfur cycle in the remote marine boundary layer. Within the 2500 m boundary layer, burden units are ng S/m and flux units are ng S/m h. Fluxes within the atmospheric layer are calculated from the burden and the residence time. Dots indicate that calculations based on independent measurements are being compared. The measured wet deposition of nss-SO " (not shown) is 13 7 //g S/m /h Inputs and outputs roughly balance, suggesting that a consistent model of the remote marine sulfur cycle within the planetary boundary layer can be constructed based on biogenic DMS inputs alone. Data (1) Andreae (1986) (2) Galloway (1985) (3) Saltzman et al. (1983) (4) sulfate aerosol lifetime calculated earlier in this chapter based on marine rainwater pH the same lifetime is applied to MSA aerosol. Modified from Crutzen et al. (1983) with the permission of Kluwer Academic Publishers.

Bandy AR, Maroulis PJ. 1980. Impact of recent measurements of OCS, CS2, and S02 in background air on the global sulfur cycle. In Shriner DS, Richmond, C, R., Lindberg SE, ed. Atmos sulfur deposition Environ Impact Health Eff Proc Life Sci Symp. 2nded. Ann Arbor, MI Ann Arbor Sci., 55-63. 

An atmospheric sulfur inventory for the whole European continent has been recently constructed by E. Meszaros et al. (1978). These authors show on the basis of the comparison of anthropogenic sulfur emission (Semb, 1978) and sulfur advection from the Atlantic that the sulfur gained by advection is small. 70-85 % of the sulfur emitted and imported is removed over the continent equally by dry (mostly in form of S02) and wet deposition. Meszaros and his associates have estimated the dry deposition of S02 by using an average European S02—S concentration calculated from data in Table 13 (3.2 /tg m-3) and a dry deposition velocity of 1cm s (Garland, 1978). The value of wet deposition was based on precipitation chemistry measurements. It follows from this quantitative calculation that Europe contributes 15-30 % of its sulfur emission to the tropospheric sulfur cycle of other areas. 

We wish now to analyze that portion of the global sulfur cycle involving atmospheric S02 and sulfate shown in Figure 22.2. We will denote the natural and anthropogenic emissions of S02 as P 0j and P 02, respectively. P Qi includes a contribution from the oxidation of reduced sulfur species to S02. S02 is removed by dry and wet deposition and oxidized to sulfate by chemical reaction. Sulfate is also removed from the atmosphere by dry and wet deposition. Our goal is to obtain estimates for the lifetimes of S02 and SO . 

ScH.l. Depositional environment schematic sulfur cycle in marine water body and upper water-sediment interface. The redox line (gray dashed perpendicular) is placed at S and relates only to the redox state of the sulfur, not the oxic or euxinic conditions. The black dashed line separates between sediment and water bodies. For the present paper, we would like to emphasize the major 8 ratio changes caused by the dissimilatory reduction of sulfate. For more detailed explanations on the formation of sulfur rich OM, see Aizenshtat et al. (1983, 1995, 2004) and Krein and Aizenshtat (1993, 1994). 

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