Coal burning, atmospheric sulfur dioxide

Apply Coal and petroleum products are sometimes contaminated with sulfur. When coal or petroleum containing sulfur is burned, sulfur dioxide (SO2) can be released into the atmosphere. Use the information about the reactions involved in industrial sulfuric-acid production to infer how atmospheric sulfur dioxide contributes to acid precipitation. 

Sulfuric acid is a component of acid rain and forms in air from sulfur dioxide, following reactions that are similar to those involved in the contact process. Atmospheric sulfur dioxide has both natural and human origins. Natural sources include plant and animal decomposition and volcanic emissions. However, the burning of coal, oil, and natural gas has been identified as a major source of acid rain pollution. After persisting in the atmosphere for some time, sulfur dioxide is oxidized to sulfur trioxide, which dissolves in rain to give H2S04(ag ). 

The sulfuric acid in acid rain is formed from sulfur dioxide in the atmosphere. Sulfur dioxide is released from volcanoes, but the majority comes from the burning of sulfur-containing fuels, primarily coal in power stations. Car exhaust emissions and the smelting of metals, such as zinc. 

The production of acid rain starts when atmospheric sulfur dioxide is oxidized to sulfur trioxide in a complex series of reactions. SO3 is, in turn, hydrolyzed to sulfuric acid. Anthropogenic sources of sulfur dioxide include the burning of coal, the refining and burning of oil, and the smelting of copper ores. Until control measures started to come on line, the pH of rainwater in the northeastern United States and other areas downwind of such sources had fallen to values between 3 and 4. The best control measures have proven to be wet and dry scrubbers. As a result of installation of these flue-gas desulfurization (FGD) devices, the amount of sulfur and nitrogen oxides released to the atmosphere has measurably decreased in the last several decades. 

Sulfur Dioxide Emissions and Control. A substantial part of the sulfur dioxide in the atmosphere is the result of burning sulfur-containing fuel, notably coal, and smelting sulfide ores. Methods for controlling sulfur dioxide emissions have been reviewed (312—314) (see also Air POLLUTION CONTROL PffiTHODS COAL CONVERSION PROCESSES, CLEANING AND DESULFURIZATION EXHAUST CONTROL, INDUSTRIAL SULFURREMOVAL AND RECOVERY). 

Another key feature of sulfur chemistry is the Lewis acidity of sulfur dioxide. Sulfur dioxide is a common atmospheric pollutant that results from burning coal to produce electricity. Most coal reserves in North America include significant amounts of sulfur-containing impurities. When coal is burned, sulfur combines with O2 to form SO2, a hard Lewis acid. 

Sulfur dioxide also exists in Earth s atmosphere. It is released by the burning of fossil fuels, such as coal and gasoline, in power plants and automobiles. Once in the atmosphere, the sulfur dioxide... 

Acid rain is actually a catchall phrase for any kind of acidic precipitation, including snow, sleet, mist, and fog. Acid rain begins when water comes into contact with sulfur and nitrogen oxides in the atmosphere. These oxides can come from natural sources such as volcanic emissions or decaying plants. But there are man-made sources as well, such as power plant and automobile emissions. In the United States, two-thirds of all the sulfur dioxide and one-fourth of the nitrogen oxides in the atmosphere are produced by coal-burning power plants. 

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. 

When coal, oil, and gas are burned for energy in power plants and in industries, sulfur dioxide is produced. Sulfur dioxide combines with water in the atmosphere to produce sulfurous acid (H2SO3). Subsequent oxidation in the presence of oxygen (air) yields sulfuric acid (H2SO4). 

Sulfurous acid (H SOj) can be produced by burning sulfur to form sulfur dioxide (SOj) gas and by then dissolving the gas in water to form sulfurous acid. This is the acid produced by burning coal that has a high sulfur content the gaseous sulfur dioxide by-product of combustion then combines with atmospheric water to form acid rain. ... 

Worldwide, the amount of energy available from coal is estimated to be about ten times greater than the amount available from all petroleum and natural gas reserves combined. Coal is also the filthiest fossil fuel because it contains large amounts of such impurities as sulfur, toxic heavy metals, and radioactive isotopes. Burning coal is therefore one of the quickest ways to introduce a variety of pollutants into the air. More than half of the sulfur dioxide and about 30 percent of the nitrogen oxides released into the atmosphere by humans come from the combustion of coal. As with other fossil fuels, the combustion of coal also produces large amounts of carbon dioxide. 

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. 

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. 

There is currently great concern about the enviromnental effects of airborne sulfur dioxide. Although SO2 is released into the atmosphere from natural sources such as volcanoes, the majority (ca. 200 million tonnes per year) is man-made either from industrial processes or domestic use such as coal and oil burning. The long-term consequences of large-scale release of SO2 into the atmosphere are undoubtedly severe, and have been the subject of much public debate. The most objectionable aspect of the problem is that often the acid rain , which results from SO2, occurs hundreds of miles from the source. 

Coal is burned in many of the world s power plants to generate electricity. Significant air pollution is produced if the stack gases from coal-fired furnaces are not treated before being released to the atmosphere. Untreated gases contain soot (fine unburned carbon particles), nitrogen oxides (NO.x), ash, and sulfur dioxide (SO2). 

Most of the sulfur dioxide in the troposphere is produced when coal and oil that contain high concentrations of sulfur are burned in power plants. The sulfur dioxide that forms is oxidized to sulfur trioxide (SO3) when it combines with either O2 or O3 in the atmosphere. When SO3 reacts with moisture in the air, sulfuric acid is formed. 

The public, unfortunately, sometimes concludes that all the emissions they perceive are pollution. Natural gas could appear to the public to be a greater pollutant than either oil or coal when, in fact, the emissions are just water vapor. The sulfur content of coal and oil can be released as sulfur dioxide to the atmosphere, and the polluting capacities of coal and oil are much greater than natural gas when all three are being burned properly. The sulfur contents as delivered to the consumers are as follows natural gas, 4 x 10 % (as added mercap-tans) number 6 fuel oil, up to 2.6% and coal, from 0.5 to 5%. In addition, coal may release particulate matter into the stack plume. 

The 25-year, effort to reduce the emissions from automobiles has greatly benefited the air quality over major cities. Even with this success, more needs to be done. None of the successful efforts has had a large impact on the emission of carbon dioxide. Many of the pollution control schemes used on automobiles actually slightly increase the emission of carbon dioxide. Burning natural gas verses coal reduces the sulfur emissions of power plants. It also slightly reduces the emission of carbon dioxide because natural gas has the least carbon and the most hydrogen of any of the fossil fuels. Unfortunately, increased use of natural gas will also increase the quantity that can escape into the atmosphere. Methane, the major component of natural gas is a potent green house gas. 

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