Sulfur oxidation in the atmosphere

Renewable energy processes do not generate sulfur dioxide, but coal-burning power plants do therefore, sulfur oxides (just as C02) are present in the atmosphere, contributing to acid rain and other hazards. The predominant form of sulfur oxide in the atmosphere is sulfur dioxide (S02) itself. Some sulfur trioxide (S03) is also formed in combustion processes, but it rapidly hydrolyzes to sulfuric acid, which is considered to be a particulate matter. In the United States, the ultimate air quality goals (secondary standards) for sulfur dioxide are 60 pg/m3 (0.02 ppm) annual arithmetic average and 260 pg/m3 (0.1 ppm) maximum 24 h concentration, which are not to be exceeded more than once a year. 

Considerable attention has been given to nitrogen oxides (and sulfur oxides) in the atmosphere because of their contributions to acid rain. Several studies suggest that different isotopic techniques can be used to differentiate among different types of atmospherically derived nitrate and ammonium. For example, Heaton (1990) found that derived from vehicle exhaust... 

Typically, the bulk of sulfur oxidation in the atmosphere occurs by heterogeneous processes in water droplets. The homogeneous oxidation of S02 to... 

The major source of sulfur oxides in the atmosphere is the burning of sulfur-containing coal in power plants. As this type of coal burns in a furnace, sulfur dioxide gas, SO2, is produced. The SO2 escapes into the atmosphere, where it reacts with more oxygen to form sulfur trioxide, SO3. 

Sulfur oxides in the atmosphere are usually present as suUurous anhydride or sulfur dioxide (SO2) and sulfuric anhydride or sulfur trioxide (SO3). Sulfur dioxide is a colourless, irritating, non-flammable, very soluble gas. It is one of the most aggressive and dangerous pollutants it derives from the oxidation of sulfur during combustion processes. Health effects of sulfur oxides are prevalently linked to respiratory system pathologies, but in high concentration they can cause asphyxiation. 

The oxidation catalyst (OC) operates according to the same principles described for a TWO catalyst except that the catalyst only oxides HC, CO, and H2. It does not reduce NO emissions because it operates in excess O2 environments. One concern regarding oxidation catalysts was the abiUty to oxidize sulfur dioxide to sulfur trioxide, because the latter then reacts with water to form a sulfuric acid mist which is emitted from the tailpipe. The SO2 emitted has the same ultimate fate in that SO2 is oxidized in the atmosphere to SO which then dissolves in water droplets as sulfuric acid. 

Sulfur oxides (SO,) are compounds of sulfur and oxygen molecules. Sulfur dioxide (SO2) is the predominant form found in the lower atmosphere. It is a colorless gas that can be detected by taste and smell in the range of 1, (X)0 to 3,000 uglm. At concentrations of 10,000 uglm , it has a pungent, unpleasant odor. Sulfur dioxide dissolves readily in water present in the atmosphere to form sulfurous acid (H SOj). About 30% of the sulfur dioxide in the atmosphere is converted to sulfate aerosol (acid aerosol), which is removed through wet or dry deposition processes. Sulfur trioxide (SO3), another oxide of sulfur, is either emitted directly into the atmosphere or produced from sulfur dioxide and is readily converted to sulfuric acid (H2SO4). 

The deleterious effect of sulfur dioxide and sulfites in domestic water is increased corrosivity owing to the lowered pH. However, oxidation of sulfite to sulfate in aqueous solutions uses dissolved oxygen, and lliis may retard corrosion. While llte oxichition of sulfite and sulfiirous acid to sulfate and sulfuric acid in the atmosphere is an environmental concern, this reaction is too... 

Precipitation over North America gradually becomes more acidic from west to east, especially in industrialized areas of the Northeast. This acid rain may be a result of the release of nitrogen and sulfur oxides into the atmosphere. The colors and numbers (see key) indicate pH measured at field laboratories in 2004. Data from National Atmospheric Deposition Program/National Trends Network http //nadp.sws.uiuc.edu. 

Figure 7.2 Acid rain occurs when water comes into contact with sulfur and nitrogen oxides in the atmosphere, which can come from natural sources or from man-made sources like cars or power plants. These acid rain-damaged coniferous trees live in the Karkonosze National Park in Silesia, Poland.

The best way to prevent these problems is to prevent acid rain at the start. Reducing emissions from automobiles and power plants would help reduce acid-rain levels. This means conserving energy and driving less. The less energy people use, the less coal needs to be burned to produce electricity. These measures help decrease the sulfur and nitrogen oxides in the atmosphere and, therefore, decrease the amount of acid rain. 

ChemicaPPhysical. Emits toxic fumes of phosphorus, nitrogen, and sulfur oxides when heated to decomposition (Sax and Lewis, 1987). Methidathion oxon was also found in fogwater collected near Earlier, CA (Glotfelty et ah, 1990). It was suggested that methidathion was oxidized in the atmosphere during daylight hours prior to its partitioning from the vapor phase into the fog. On 12 January 1986, the distributions of parathion (0.45 ng/my in the vapor phase, dissolved phase, air particles, and water particles were 57.5, 25.4, 16.8, and 0.3%, respectively. For methidathion oxon (0.84 ng/m3), the distribution in the vapor phase, dissolved phase, air particles, and water particles were <7.1, 20.8, 78.6, and 0.1%, respectively. 

Biogenic processes, however, emit reduced forms of sulfur, including dimethyl sulfide and hydrogen sulfide, with lesser amounts of carbon disulfide (CS2), dimethyl disulfide (CH3SSCH3), carbonyl sulfide (COS), and methyl mercaptan (Cl I3SH). These reduced sulfur compounds are then oxidized in the atmosphere as described in detail in Chapter 8.E. 

Calvert, J. G., and W. R. Stockwell, Mechanism and Rates of the Gas Phase Oxidations of Sulfur Dioxide and Nitrogen Oxides in the Atmosphere, in S02, NO and N02 Oxidation Mechanisms Atmospheric Considerations (J. G. Calvert, Ed.), Acid Precipitation Series, Vol. 3, pp. 1-62 (J. I. Teasley, Series Editor), Butterworth, Stoneham, MA, 1984. 

Sulfur dioxide is slowly oxidized in the atmosphere to S03, which dissolves in rainwater to give sulfuric acid. The burning of sulfur-containing fuels is thus a major cause of acid rain (Section 9.9). In the laboratory, S02 is conveniently prepared by treating sodium sulfite with dilute acid ... 

Formerly, the sulfur dioxide by-product was a source of acid rain because it is oxidized in the atmosphere to SO3, which reacts with water vapor to yield sulfuric acid. In modern roasting facilities, however, the SO2 is converted to sulfuric acid rather than being vented to the atmosphere. 

DMS is photochemically oxidized in the atmosphere to methanesulfonic and sulfuric acids. These strong acids contribute, along with nitric and organic acids, to the natural acidity of precipitation. Recent problems with acid rain have aroused interest in the anthropogenic and natural sources of volatile sulfur compounds (2). 

The factors that influence corrosion of steels in soils are the type of soil moisture content and the position of the water table soil resistivity and soluble ion content soil pH oxidation-reduction potential and the role of microbes present in soil. The exposure of a buried pipe to the soil environment is illustrated in Figure 4.2. The steel pipe is exposed to both meteoric water passing through ground surface and the water in the ground. The meteoric water may be acidic due to the presence of carbon dioxide and sulfur dioxide in the atmosphere. The soil water may be acidic in addition to some dissolved minerals. The steel pipe is partially above the water table with the rest below the water. The pH and the dissolved ions in the ground water provide a corrosive environment. 

Calvert, J. G. Stockwell, W. R. Mechanism and rates of the gas-phase oxidations of sulfur dioxide and nitrogen oxides in the atmosphere. In S02> NO and NO2 Oxidation Mechanisms Atmospheric Considerations Calvert, J. G., Ed. Butterworth Boston, 1984 pp. 1-62. 

Sulfur dioxide is oxidized in the atmosphere mainly within clouds, fogs and other aqueous-phase domains. The primary pathway [111-115] involves oxidation with H2O2 however, other reaction pathways are viable depending on pH. Some of the direct and indirect photochemical reactions of interest related to the fate of SO2 in the atmosphere include ... 

Sulfur dioxide from the combustion of sulfur-containing fossil fuels (e.g., diesel oil and coal) is oxidized in the atmosphere to form sulfur trioxide that reacts with water to form sulfuric acid. 

However, this reaction is very slow in the absence of a catalyst. One of the mysteries during early research on air pollution was how the sulfur dioxide produced from the combustion of sulfur-containing fuels is so rapidly converted to sulfur trioxide in the atmosphere. It is now known that dust and other particles can act as heterogeneous catalysts for this process (see Section 15.9). In the preparation of sulfur trioxide for the manufacture of sulfuric acid, either platinum metal or vanadium(V) oxide (V205) is used as a catalyst, and the reaction is carried out at approximately 500°C, even though this temperature decreases the value of the equilibrium constant for this exothermic reaction. 

Tanaka N., Rye D. M., Xiao Y., and Lasaga A. C. (1994) Use of stable sulfur isotope systematics for evaluating oxidation pathways and in-cloud-scavenging of sulfur dioxide in the atmosphere. Geophys. Res. Lett. 21, 1519-1522. 

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