Sulfur oxides, 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 ... 

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. 

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... 

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. 

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. 

Mass-independent fractionation, is less common and represents the processes whereby fractionations take place in a different manner from the simple proportionality predicted on the basis of atomic mass differences. This is particularly important in atmospheric chemistry, for it has been shown in laboratory experiments that, for example, the photochemical oxidation of sulfur in the atmosphere can lead to... 

Figure 19.12 Formation of acidic precipitation. A complex interplay of human activities, atmospheric chemistry, and environmental distribution leads to acidic precipitation and its harmful effects. Car exhaust and electrical utility waste gases contain lower oxides of nitrogen and sulfur. These are oxidized in the atmosphere by O2 (or O3, not shown) to higher oxides (NO2, SO3), which react with moisture to form acidic rain, snow, and fog. In contact with acidic precipitation, many lakes become acidified, whereas limestone-bounded lakes form a carbonate buffer that prevents acidification.

Another interesting example of the biological influence on atmospheric chemistry is provided by sulfur. Under natural conditions, sulfur compounds in the atmosphere are provided by the oceanic emission of dimethyl disulfide (DMS). This biogenic emission results from the breakdown of sulfoniopropionate (DMSP), which is thought to be used by marine phytoplankton to control their osmotic pre.ssure. The oxidation of DMS leads to the formation of sulfur dioxide, which is further converted to sulfate particles. As indicated above, these particles, by scattering back to space some of the incoming solar radiation, tend to cool the earth s surface. Their presence also affects the optical properties of the clouds, which introduces an indirect climatic effect. 

Once the importance of DMS to the global sulfur cycle was established, numerous measurements of DMS concentrations in the marine atmosphere have been conducted. The average DMS mixing ratio in the marine boundary layer (MBL) is in the range of 80-1 lOppt but can reach values as high as 1 ppb over entrophic (e.g., coastal, upwelling) waters. DMS mixing ratios fall rapidly with altitude to a few parts per trillion in the free troposphere. After transfer across the air-sea interface into the atmosphere, DMS reacts predominantly with the hydroxyl radical and also with the nitrate (N03) radical. Oxidation of DMS is the exclusive source of methane sulfonic acid (MSA) in the atmosphere, and the dominant source of S02 in the marine atmosphere. We will return to the atmospheric chemistry of DMS in Chapter 6. 

ATMOSPHERIC CHEMISTRY (GAS PHASE) OF SULFUR COMPOUNDS 6.13.1 Sulfur Oxides... 

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 ... 

Nahir, T. M. and G A. Dawson (1987) Oxidation of sulfur dioxide by ozone in highly dispersed water droplets. Journal of Atmospheric Chemistry 5, 373-383 Nakamura, T. (2005) Post-hydration thermal metamorphism of carbonaceous chondrites. 

I learned about gases such carbon dioxide, nitrogen oxide, sulfur dioxides from chemistry lessons. I think these gases pollute the environment. I am not sure about greenhouses gases. I think the factories are the main reason for these gases in the atmosphere and these factories should be banned from operating. 

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