Atmosphere sulfate oxidation

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 ... 

FIGURE 3-26 Atmospheric SO, oxidation to aerosol sulfate homogeneous gas phase organic reactions. 

In the upper atmosphere such oxidation of sulfur dioxide to its trioxide forming sulfuric acid or sulfate anion may occur at ambient temperature at a much slower rate in the presence of various free radicals. 

Although limited, the data suggest that DMS from marine phytoplankton would most likely be enriched in the heavier isotope and would have a 634S value slightly less than seawater sulfate as a result of ASR. Until the 634S values for seawater DMS, remote SO2 and sulfate are actually measured or until the uncertainties which surround the removal pathways for DMS and its atmospheric oxidation are addressed, questions remain as to the i S value of atmospheric sulfate from this source. 

Elemental Sulfur. In 1942, Chatterjee (44) reported the presence of elemental sulfur in weathered Indian coal but not in fresh samples. He suggested that, during weathering, pyrite is first oxidized to ferrous and ferric sulfates, and that then ferric sulfate oxidizes pyrite to elemental sulfur. The presence of elemental sulfur in U.S. coals was confirmed recently by Richard et al. (45) and White and Lee (46). Duran et al. (47) used extraction and gas chromatographic analysis to determine elemental sulfur in a suite of U.S. coals. They found that elemental sulfur (0.03-0.17%) is present in coal that has been exposed to the atmosphere, but is absent in pristine samples that have been processed and sealed under a nitrogen atmosphere. These data support Chatteijee s discovery that elemental sulfur in coal is a weathering product. 

The discovery of the anomalous oxygen isotopic compositions of atmospheric sulfate provides a new means for identifying sulfate of atmospheric origin. Rainwater and aerosols from southern California were found to have A O values in the range of 0%o to -K.5%o (Lee et al., 2001). The average A O of snow sulfate in the Rocky Mountains (Colorado, USA) was - -1.3%o. Sulfate in ice cores, massive sulfate deposits, and Dry Valley soils from various locations also have MIF (Bao et al., 2000 Lee et al., 2001). There appears to be seasonality in the A O of sulfate in precipitation, with higher values in the winter and lower values in the summer, probably due to seasonal changes in climatic elfects that favor aqueous phase S(IV) oxidation in winter relative to summer (Lee and Thiemens, 2001). 

Ash consists of mineral material compounds, which include clays, silicates, carbonates, sulfides, sulfates, oxides, and phosphates. Major elements are Al, Si, Ca, and Fe minor elements are K, Na, Mg, and others trace elements are As, Be, Hg, etc. The mineral matter influences fouling, slagging, and heat transfer in high-temperature furnaces the performance of particulate control equipment and the health and ecological effect of particles escaping to the atmosphere.22... 

Sulfide methylation reactions couple dissimilatory sulfate reduction to DMS production and determine the rates of DMS emission in freshwater wetlands. This process involves acetogenic bacteria, some of which degrade aromatic acids to acetone. In soils, freshwater, and marine ecosystems a wide diversity of other anaerobic and aerobic bacteria can contribute to sulfur gas production. In addition, diverse aerobes (e.g. methylotrophs and sulfate oxidizers) and anaerobes (e.g. methanogenes) consume S gas, thereby regulating fluxes in the atmosphere-biosphere system. 

It is well known that SO anions stimulate corrosion of steel surfaces by preventing an in situ formation of iron oxides, which may impede the diffusion processes involved in the corrosion reactions. These sulfate anions are either formed in the atmosphere by oxidation of SO or by direct reaction with the steel surface in the presence of water to form so-called sulfate nests. The latter transformation may take place at the unprotected metal surface or possibly, at least in principal, after SO2 has permeated the organic film and arrived at the metal support. The diffusion of SO anions through organic coatings seems... 

Sulfide oxidation in a carbonate environment involves two sets of reactions oxidation and neutralization. Sulfide minerals exposed to the atmosphere can oxidize to produce sulfate and acidity (Equation 1) ... 

Atmospheric reactions modify the physical and chemical properties of emitted materials, changing removal rates and exerting a major influence on acid deposition rates. Sulfur dioxide can be converted to sulfate by reactions in gas, aerosol, and aqueous phases. As we noted in Chapter 17, the aqueous-phase pathway is estimated to be responsible for more than half of the ambient atmospheric sulfate concentrations, with the remainder produced by the gas-phase oxidation of S02 by OH (Walcek et al. 1990 Karamachandani and Venkatram 1992 Dennis et al. 1993 McHenry and Dennis 1994). These results are in agreement with box model calculations suggesting that gas-phase daytime S02 oxidation rates are l-5% per hour, while a representative in-cloud oxidation rate is 10% per minute for 1 ppb of H202. 

The idealized calculation just presented shows what are thought to be the essential elements of the aqueous-phase chemistry of acid rain. Measurements of H2O2 in rain and cloudwater show a range of concentrations between approximately 10 and 1(X) /itM (Kok, 1980 Zika et al., 1982). Water with this composition is in equilibrium with between 0.1 and 1.0 ppb gas-phase H2O2. Kleinman (1984) has examined the question of whether H2O2 can account for the in-cloud oxidation of SO2 and found that under summertime conditions between 3 and 5 ppb of H2O2 would be required to account for estimated incloud sulfate formation. Seigneur et al. (1984) presented the results of simulations of atmospheric sulfate and nitrate formation by both gas- and aqueous-phase paths under... 

Interestingly, it has been found that the formation of SOA is accelerated in the presence of SO2 and sulfuric acid (Jang et al. 2002, Edney et al. 2005, Surrat et al. 2007). The first step in atmospheric SO2 oxidation is OH addition (Chapter 5.5.2.1) and this radical can react with alkoxy radicals (RO) to form sulfonic acid and further with organic peroxo radicals to form dialkyl sulfates ... 

The atmospheric chemistry of sulfur is simpler than that of nitrogen in two aspects. First, the number of stable species in air is smaller and second, the variety of interactions in the climate system is less - almost all effects come from sulfate, such as acidity and radiation scattering. In the oxidation line to sulfate, oxidants are consumed ... 

Because of the importance of SO2 and sulfate in the atmosphere, the oxidation pathways in solution have been studied extensively and typically been subdivided as follows ... 

The last question is important because not only does the percentage of atmospheric SO2 oxidation (often global climate models assume a simple conversion factor in percentage of SO2 emission) determine the climate active sulfate but so does the particulate sulfate in air. Fig. 5.31 shows a scheme of the multiphase atmospheric sulfur chemistry. The figures are derived from many field studies and modeling attempts, and are representative of Europe. It is noteworthy that the number of... 

Because of overmanuring of agricultural land, the ammonia content of the air has increased noticeably for example, by a factor of 2-3 in rainwater in the United Kingdom between 1%8 and 1978 (Martin and Barber, 1978). Ammonia in atmospheric quantities does not accelerate zinc corrosion, and petrochemical plants where ammonium salts are present show no accelerated attack on galvanized steel. However, ammonia will react with atmospheric sulfur oxides, yielding ammonium sulfate, which accelerates paint film corrosion and also zinc corrosion. 

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