Global Sulfur

Figure 13-6a (Ivanov, 1983) is a depiction of the natural global sulfur budget. Figure 13-6b depicts the budget with natural and anthropogenic sources. Table 13-2 serves to explain Fig. 13-6 and includes the wide range of estimates of various fluxes, and demonstrates the degree of uncertainty inherent in such approaches.

Friend,. P. (1973). The global sulfur cycle. In Chemistry of the Lower Atmosphere" (S. I. Rasool, ed.). Plenum Press, New York. 

In simple terms, the global sulfur cycle has two components. One is biochemical involving the conversion of sulfate to sulfide and the formation of DMS the other is atmospheric photochemical oxidation of DMS to sulfur oxyacids. DMS is formed mainly in the oceans by microorganisms and to a lesser extent in plants. About 38M0 Tg year-1 of DMS are released to the atmosphere from the oceans. The major precursor for DMS formation is the sulfonium salt, dimethylsulfoniopropionate, (CH3)2 S+ CH2 CH2 COOH, DMSP. DMSP lyase enzymes catalyze an elimination of acrylic acid from DMSP (Equation 12) with the release of DMS ... 

Malin G (1996) The role of DMSP and DMS in the global sulfur cycle and climate regulation. In Kiene RP, Visscher P, Keller M, Kirst GO (eds) Biological and environmental chemistry of DMSP and related sulfonium compounds. Plenum, New York, pp 177-189 Malin G (1997) Sulphur, climate and the microbial maze. Nature 387 857-859 Malin G, Kirst GO (1997) Algal production of dimethyl sulfide and its atmospheric role. J Phycol 33 889-896... 

Table 8.7 Estimates of global sulfur emissions (Tg S year )... 

Sulfonium compounds occur in a wide range of unicellular algae as well as red algae. They have been shown to be the major source of atmospheric sulfur compounds such as dimethyl sulfide and from methanethiol from the ocean, which has a central role ir he global sulfur cycle [143]. 

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. 

Lower terrestrial and coastal emission estimates combined with the increasing loss in wetlands 165-681. although it may not significantly impact the global sulfur cycle, may be an important consideration in local contributions of natural emissions to acid precipitation. 

The first report of DMS in the ocean appeared in 1972 (22.)- The authors suggested that DMS might be more important than H2S as a biogenic sulfur source for balancing the global sulfur budgets. Preliminary estimates of DMS sea-to-air flux based on the limited data were made by Liss and Slater (741. 

Models of the global sulfur cycle include biological sources of volatile sulfur... 

COS, S02 and CO are all potential end products of reaction (2), and its mechanism and relative yields are of great importance in assessing the role of reaction (1) in the global sulfur cycle. We have identified thirteen exothermic channels for (2), three of which, (2c), (2g) and (2j), regenerate the OH molecule and would not be measured in our expenments. 

The DMS emissions from the ocean represent a significant part of the global sulfur flux to the atmosphere. It might be of particular interest to find new reaction routes which couple biogenic emissions from the sea to the chemistry of tropospheric photooxidants by which important properties of the atmosphere are regulated. 

Induction of chemokinetic ability also occurs in Alcaligenes strain M3A.60 Dimethyl sulfonio-propionate (DMSP) is an attractant for bacteria that have been induced to produce DMSP lyase. Such cells are attracted to DMSP at ecologically relevant concentrations, but uninduced cells do not respond to DMSP. Since DMSP lyase produces dimethylsulfide, which is important to global climate regulation, Zimmer-Faust et al.60 suggest that bacterial chemokinesis may play a critical role in global sulfur cycles and climate. 

Included in Table I are molybdenum enzymes that are as yet unclassified due to their partial characterization (46—49, 58). These enzymes includes polysulfide reductase that accomplish sulfur reduction to sulfide (46), underlining its role in the global sulfur cycling. Chlorate and selenate reductase are examples of relatively rare enzymes using simple oxyanions of third-row elements as substrates (47 19, 58). 

Dimethyl sulfoxide reductases (DMSOR) of bacteria and fungi that catalyze the reduction of DMSO to dimethyl sulfide (DMS). These enzymes play a significant role in the global sulfur cycle, not least because DMS is volatile and is the precursor of the methylsulfonate aerosols that nucleate cloud formation (29). Furthermore, the distinctive smell of DMS acts as a guide to certain seabirds who use it to locate productive regions of the ocean (30). 

All the effective SC>2 oxidation reactions mentioned so far are applicable only in polluted environments and are most likely heterogeneous. While these reactions may be important for the global sulfur balance since combustion is a large source of atmospheric sulfur, they are not significant SC oxidation reactions in the normal troposphere. There are, however, a number of homogeneous gas-phase reactions to consider. 

My presentation here on the global sulfur budget has been very much facilitated as I earlier this year received from Professor M.V. Ivanov a monograph (not yet published in English) with the following title The global biogeochemical sulfur cycle and influence on it of human activity ( ). 

In a paper from 1978 (Atm. Env. Vol. 12), H. Rhode points out that making estimates of the global sulfur budget can be formulated as seeking answers to the following two questions earlier presented in a paper by Kellog et al. (Science 17, pp. 587-596, 1972) ... 

Fig. 1. The global sulfur budget. (Figures in brackets indicate anthropogenic contributions).

The total global sulfur budget and the transfer processes of sulfur... 

Using the data in the Tables 6-11 and also data concerning the liquid and solid phases and with the application of the model in Fig. 1, the authors of the monograph have finally arrived at an estimation of the total global sulfur budget. It is presented in Figure 2. 

H2O, CO, OCS, and SO have spatially and temporally variable abundances. Variations in the abundances of water vapor, CO, and sulfur gases are of particular interest because they result from the solar UV-diiven photochemistry that maintains the global sulfuric acid cloud cover. 

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