Sulfur trioxide, atmosphere

Selenium trioxide, SeO, is white, crystalline, and hygroscopic. It can be prepared by the action of sulfur trioxide on potassium selenate or of phosphorous pentoxide on selenic acid. It forms selenic acid when dissolved in water. The pure trioxide is soluble in a number of organic solvents. A solution in Hquid sulfur dioxide is a selenonating agent. It is stable in very dry atmospheres at room temperature and on heating it decomposes first to selenium pentoxide [12293-89-9] and then to selenium dioxide. 

Chemical Properties. The chemistry of the sulfur chlorides has been reviewed (141,142). Sulfur monochloride is stable at ambient temperature but undergoes exchange with dissolved sulfur at 100°C, indicating reversible dissociation. When distilled at its atmospheric boiling point, it undergoes some decomposition to the dichloride, but decomposition is avoided with distillation at ca 6.7 kPa (50 mm Hg). At above 300°C, substantial dissociation to S2 and CI2 occurs. Sulfur monochloride is noncombustible at ambient temperature, but at elevated temperatures it decomposes to chlorine and sulfur (137). The sulfur then is capable of burning to sulfur dioxide and a small proportion of sulfur trioxide. 

Sulfur Trioxide. Pure sulfur trioxide [7446-11-9] at room temperature and atmospheric pressure is a colorless Hquid that fumes in air. This material can exist in both monomeric and polymeric forms. In the gaseous and Hquid state pure SO is an equiHbrium mixture of monomeric SO and... 

A solution of sulfur trioxide [7446-11-9] dissolved in chlorosulfonic acid [7990-94-5] CISO H, has been used as a smoke (U.S. designation FS) but it is not a U.S. standard agent (see Chlorosulfuric acid Sulfuric acid and sulfur trioxide). When FS is atomized in air, the sulfur trioxide evaporates from the small droplets and reacts with atmospheric moisture to form sulfuric acid vapor. This vapor condenses into minute droplets that form a dense white cloud. FS produces its effect almost instantaneously upon mechanical atomization into the atmosphere, except at very low temperatures. At such temperatures, the small amount of moisture normally present in the atmosphere, requires that FS be thermally generated with the addition of steam to be effective. FS can be used as a fill for artillery and mortar shells and bombs and can be effectively dispersed from low performance aircraft spray tanks. FS is both corrosive and toxic in the presence of moisture, which imposes limitations on its storage, handling, and use. 

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). 

Alternatively, in the presence of particulate matter and aerosols, sulfur dioxide may react with atmospheric oxygen to form sulfur trioxide, which forms sulfuric acid, a strong acid, in water ... 

The sulfur dioxide in Venus atmosphere is turned into sulfuric acid by two different chemical reactions. In the first reaction, the sulfur dioxide reacts with oxygen to form sulfur trioxide ... 

Smelting releases sulfur dioxide gas from a metal sulfide ore. Before the twentieth century, most of the sulfur dioxide expelled in the smelting process poured out of the factory s smokestacks directly into the atmosphere. Sulfur dioxide in the atmosphere, however, is a powerful greenhouse gas. Today, most of the hot sulfur dioxide gas released in the smelting process is captured, cooled, cleaned, and converted into sulfur trioxide ... 

Acid rain is caused primarily by sulfur dioxide emissions from burning fossil fuels such as coal, oil, and natural gas. Sulfur is an impurity in these fuels for example, coal typically contains 2-3% by weight sulfur.1M Other sources of sulfur include the industrial smelting of metal sulfide ores to produce the elemental metal and, in some parts of the world, volcanic eruptions. When fossils fuels are burned, sulfur is oxidized to sulfur dioxide (SO2) and trace amounts of sulfur trioxide (SC>3)J21 The release of sulfur dioxide and sulfur trioxide emissions to the atmosphere is the major source of acid rain. These gases combine with oxygen and water vapor to form a fine mist of sulfuric acid that settles on land, on vegetation, and in the ocean. 

Oil of vitriol was prepared by heating a natural vitriol, most typically green (iron) vitriol. This yielded sulfur trioxide which combined with the moisture of the air to give a fairly concentrated sulfuric acid. The name, oil of vitriol, was derived from its source, and from its viscous nature. Acid (or spirit) of sulfur was made by the combustion of common sulfur, the sulfur dioxide produced reacted with the moisture and the oxygen of the atmosphere to give a much more dilute solution of the same acid, mixed with some unoxidized sulfur dioxide. 

At atmospheric pressure, sulfuric acid has a maximum boiling azeotrope at approximately 98.48% (78,79). At 25°C, the minimum vapor pressure occurs at 99.4% (78). Data and a discussion on the azeotropic composition of sulfuric acid as a function of pressure can also be found in these two references. The vapor pressure exerted by sulfuric acid solutions below the azeotrope is primarily from water vapor above the azeotropic concentration S03 is the primary component of the vapor phase. The vapor of sulfuric acid solutions between 85% H2S04 and 35% free S03 is a mixture of sulfuric acid, water, and sulfur trioxide vapors. At the boiling point, sulfuric acid solutions containing <85% H2S04 evaporate water exclusively those containing >35% free S03 (oleum) evaporate exclusively sulfur trioxide. 

Sulfur dioxide, sulfur trioxide, and various oxides of nitrogen are generated by coal-burning power plants. They dissolve in water in the atmosphere to produce the acid rain downwind of industrial centers. 

The primary cause of acid rain is industrial and automotive pollution. Each year in industrialized countries, large power plants and smelters that burn sulfur-containing fossil fuels pour millions of tons of sulfur dioxide (S02) gas into the atmosphere, where some is oxidized by air to produce sulfur trioxide (S03). Sulfur oxides then dis-l solve in rain to form dilute sulfurous acid and sulfuric acid ... 

The dilute acid was then concentrated at atmospheric pressure, producing a reusable acid but also a number of troublesome by-products. Sulfur trioxide vapor was produced as the acid became more concentrated. This produced an intolerable fog, so electrostatic precipitators were installed and the remaining vapor was decomposed by heat into sulfur dioxide which was discharged from a high stack. 

C Even though an increase in pressure increases the yield of sulfur trioxide, the reaction in the converter is carried out at atmospheric pressure. Suggest a reason for this. 

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. 

Sulfur trioxide gas, one of the causes of acid rain, is produced in the upper atmosphere when oxygen reacts with sulfur dioxide gas in the reaction shown below ... 

While the current catalyst screening is done at atmospheric pressure, commercial reactors would operate at pressures up to perhaps 20 atmospheres. The effect of pressure on the decomposition kinetics has to be explored. Therefore, a pressurized catalytic sulfur trioxide reduction reactor has been designed and plans for its construction and operation have been made. 

Gas phase molecular aggregates that contain acid molecules have been produced with free jet expansion techniques and detected by using electron impact ionization mass spectrometry. The clusters of aqueous nitric acid paralleled many properties of the condensed phase. Multiple nitric acid molecules were found in the clusters that were sufficiently dilute. The acid molecule was absent in the ionized clusters involving HC1 and only water was evident. Experiments also demonstrated the reactivity of ammonia with aqueous nitric acid and sulfur dioxide clusters and of sulfur trioxide with water clusters. The natural occurrence of acid cluster negative ions offers a means to probe the gas phase acid loading of the atmosphere through laboratory and field studies of the ion chemistry. 

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. 

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