Sulfur atmospheric chemistry

Sulfur forms several oxides that in atmospheric chemistry are referred to collectively as SOx (read sox ). The most important oxides and oxoacids of sulfur are the dioxide and trioxide and the corresponding sulfurous and sulfuric acids. Sulfur burns in air to form sulfur dioxide, S02 (11), a colorless, choking, poisonous gas (recall Fig. C.1). About 7 X 1010 kg of sulfur dioxide is produced annually from the decomposition of vegetation and from volcanic emissions. In addition, approximately 1 X 1011 kg of naturally occurring hydrogen sulfide is oxidized each year to the dioxide by atmospheric oxygen ... 

Bates TS, Lamb B, Guenther A, Dignon J, Stoiber R (1992) Sulfur emissions to the atmosphere from natural sources. J Atmos Chem 14 315-337 Bischoff B, Karsten U, Daniel C, Kuck K, Xia B, Wiencke W (1994) Preliminary assessment of the beta-dimethylsulfoniopropionate (DMSP) content of macroalgae from the tropical island Hainan (People s Republic of China). Aust J Mar Freshwater Res 45 1329-1336 Bolser RC, Hay ME (1996) Are tropical plants better defended Palatability and defenses of temperate vs. tropical seaweeds. Ecology 77 2269-2286 Brasseur G, Orlando J, Tyndall G (1999) Atmospheric chemistry and global change. Oxford, New York... 

Historically, the sulfur oxides have long been known to have a deleterious effect on the atmosphere, and sulfuric acid mist and other sulfate particulate matter are well established as important sources of atmospheric contamination. However, the atmospheric chemistry is probably not as well understood as the gas-phase photoxidation reactions of the nitrogen oxides-hydrocarbon system. The pollutants form originally from the S02 emitted to the air. Just as mobile and stationary combustion sources emit some small quantities of N02 as well as NO, so do they emit some small quantities of S03 when they bum sulfur-containing fuels. Leighton [2] also discusses the oxidation of S02 in polluted atmospheres and an excellent review by Bulfalini [3] has appeared. This section draws heavily from these sources. 

Kreidenweis, S. M., and J. H. Seinfeld, Nucleation of Sulfuric Acid-Water and Methanesulfonic Acid-Water Solution Particles Implications for the Atmospheric Chemistry of Organosulfur Species, Atmos. Environ., 22, 283-296 (1988a). 

Maahs, H. G., Sulfur-Dioxide/Water Equilibria between 0° and 50°C An Examination of Data at Low Concentrations, in Heterogeneous Atmospheric Chemistry (D. R. Schryer, Ed.), pp. 187-195, Geophysical Monograph 26, Am. Geophys. Union, Washington, DC, 1982. 

One means to assess the relative contributions of the various sources of sulfur to the atmosphere is through the use of sulfur isotope ratios (12-16). Isotopic ratios may be used as source tracers if 1) the isotopic composition of the sources as they enter the atmosphere are known, 2) the isotopic compositions of the various sources are different from one another, and 3) the isotopic changes that occur during biological, physical and/or chemical transformations are understood. Presently, isotopic data for sulfur compounds in the remote atmosphere (Table I) are limited. However, collection and analytical techniques are now available to make isotopic measurements of the critical species. In the text that follows, various aspects of sulfur isotope chemistry will be discussed. 

Atmospheric Considerations. It is probably premature to assess the role of liquid phase oxidation of reduced sulfur compounds in atmospheric chemistry with the limited kinetic data available in the open literature. However, it is appropriate to discuss certain conclusions obvious from the information presented above. 

The catalytic oxidation of sulphurous acid in aqueous medium to sulphuric acid [138, 84] has been suggested as a probe reaction for the ability of a carbon to activate molecular oxygen at ambient conditions. Besides this remarkable property the reaction is of interest in atmospheric chemistry where it provides a sink for all nonphotochemically oxidized sulfur dioxide [215]. Carbon plays a special role in this environmental application as both pure carbon and active particles (iron oxide [84] for example) anchored to carbon can act as efficient catalysts. The detailed analysis of the reactivity of various types of carbon [138] reveal that basic surface oxides (see Fig. 23) are important to fix the educt HSOj ion. It was found, in addition, that the... 

Seinfeld, J.H. 1986. Atmospheric Chemistry and Physics of Air Pollution. New York Wiley. Sheppard, D. 1988. Mechanisms of airway responses to inhaled sulfur dioxide. Pp. 49— 65 in Pathophysiology and Treatment of Inhalation Injuries, Lung Biology in Health and Disease, Vol. 34., J.Loke, ed. New York, NY Marcel Dekker. 

Gas-phase, solution-phase, and heterogeneous reactions all play important roles in atmospheric chemistry. The mean atmospheric composition is given in Table 1. N2, O2, and Ar comprise 99.9% of the atmosphere and, for all practical purposes, the relative proportion of these gases is constant in the lower 100 km of the atmosphere. We are concerned here with the fate of pollutants such as CO, volatile organic compounds, halocarbons, sulfur compounds, and nitrogen oxides, which are present in trace amounts and whose concentrations vary significantly both spatially and temporally. 

Oxygenated Sulfur Radicals Relevant to Atmospheric Chemistry. .111... 

The tropospheric sulfur chemistry is different. Unlike the nitrogen and carbon chemistry, where combustion is an insignificant source, the combustion source of SO2 appears to be very important. While OH reactions can be shown to convert sulfides to SO2, it is not clear that normal atmospheric chemistry is important in the next step—the conversion of S02 to H2SO, which is then removed from the atmosphere by rainout. It has also been suggested that a large amount of SO2 is removed directly by rainout. Unfortunately we have the fewest data, both kinetic and atmospheric, on sulfur compounds. Most of the kinetic data we do have are at high temperatures, and most of the atmospheric data are for polluted environments. 

Cadle, R. D., Atmospheric Chemistry of Chlorine and Sulfur Compounds, ... 

Oxidation of sulfur-bearing gases in the atmosphere can lead to non-mass-dependent isotopic fractionation, manifested as excesses or deficiencies in Farquhar et al. (2000) found small deficits in a nakhlite, and proposed that this was an isotopic signature of martian atmospheric chemistry. This subtle non-mass-dependent signal was not seen in other martian samples, but it bolsters the idea that outgassed volatiles are fractionated in the atmosphere and then returned to the lithosphere. 

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