Sulfur dioxide acid rain

Rainwater is naturally slightly acidic due to the dissolved carbon dioxide. Acid rain results when acidic sulfur and nitrogen oxides produced during the combustion of coal and oil react with rainwater (see Box 10.1). 

Elsewhere acid deposition tends to be more of a local problem. For example, in the western states, oxides of nitrogen produced by motor vehicles are a more important source of acid rain than is sulfur dioxide. Acid deposition in California, then, is more a consequence of extensive automobile traffic than of power generation. 

As worldwide attention has been focused on the dangers of acid rain, the demand to reduce sulfur dioxide [7446-09-5] emissions has risen. Several processes have been developed to remove and recover sulfur dioxide. Sulfur can be recovered from sulfur dioxide as Hquid sulfur dioxide, sulfuric acid, or elemental sulfur. As for the case of hydrogen sulfide, sulfur dioxide removal processes are categorized as adsorption, absorption, or conversion processes. 

Municipal incinerators are often targeted as a primary cause of acid rain. In fact, power plants burning fossil fuels, which produce sulfur dioxide and nitrogen oxide, are actually the leading cause of acid rain, along with automotive exhaust (176,177). In Europe and Japan, studies show that only about 0.02% of all acid rain can be traced to incineration of PVC (178). 

Flue Ga.s Desulfuriza.tion. Citric acid can be used to buffer systems that can scmb sulfur dioxide from flue gas produced by large coal and gas-fired boilers generating steam for electrical power (134—143). The optimum pH for sulfur dioxide absorption is pH 4.5, which is where citrate has buffer capacity. Sulfur dioxide is the primary contributor to acid rain, which can cause environmental damage. 

Acid deposition occurs when sulfur dioxide and nitrogen oxide emissions are transformed in the atmosphere and return to the earth in rain, fog or snow. Approximately 20 million tons of SOj are emitted annually in the United States, mostly from the burning of fossil fuels by electric utilities. Acid rain damages lakes, harms forests and buildings, contributes to reduced visibility, and is suspected of damaging health. 

High concentrations of SO, can produce tempo-rai y breathing difficulties in asthmatic children and in adults who are active outdoors. Sulfur dioxide also can directly damage plants and has been shown to decrease crop yields. In addition, sulfur oxides can be converted to sulfuric acid and lead to acid rain. Acid rain can harm ecosystems by increasing the acidity of soils as well as surface waters such as rivers, lakes, and streams. Sulfur dioxide levels fell, on average, by 39 percent between 1989 and 1998. 

Burning fossil fuels can release air pollutants such as carbon dioxide, sulfur oxides, nitrogen oxides, ozone, and particulate matter. Sulfur and nitrogen oxides contribute to acid rain ozone is a component of urban smog, and particulate matter affects respiratory health. In fact, several studies have documented a disturbing correlation between suspended particulate levels and human mortality. It is estimated that air pollution may help cause 500,000 premature deaths and millions of new respiratory illnesses each year. 

Public concerns about air quality led to the passage of the Clean Air Act in 1970 to amendments to that act in 1977 and 1990. The 1990 amendments contained seven separate titles covering different regula-toiy programs and include requirements to install more advanced pollution control equipment and make other changes in industrial operations to reduce emissions of air pollutants. The 1990 amendments address sulfur dioxide emissions and acid rain deposition, nitrous oxide emissions, ground-level ozone, carbon monoxide emissions, particulate emissions, tail pipe emissions, evaporative emissions, reformulated gasoline, clean-fueled vehicles and fleets, hazardous air pollutants, solid waste incineration, and accidental chemical releases. 

Sulfur dioxide emissions resulting from fossil fuel can have negative effects on urban air quality and create acid rain that harms aquatic life. These emissions arc nonexcludable in that there is no private action that a particular individual can take to avoid this impact, and they are nonrival in that their effect on any one individual does not preclude or offset their effect on any other. 

Natural gas will continue to be substituted for oil and coal as primary energy source in order to reduce emissions of noxious combustion products particulates (soot), unburned hydrocarbons, dioxins, sulfur and nitrogen oxides (sources of acid rain and snow), and toxic carbon monoxide, as well as carbon dioxide, which is believed to be the chief greenhouse gas responsible for global warming. Policy implemented to curtail carbon emissions based on the perceived threat could dramatically accelerate the switch to natural gas. 

The sulfuric acid forms as tiny droplets high in the atmosphere. These may be carried by prevailing winds as far as 1500 km. The acid rain that falls in the Adirondacks of New York (where up to 40% of the lakes are acidic) comes from sulfur dioxide produced by power plants in Ohio and Illinois. 

About half the manmade emissions of sulfur dioxide become sulfate aerosol. That implies that currently 35 Tg per year of sulfur in sulfur dioxide is converted chemically to sulfate. Because the molecular weight of sulfate is three times that of elemental sulfur, Q is about 105 Tg per year. Studies of sulfate in acid rain have shown that sulfates persist in the air for about five days, or 0.014 year. The area of the Earth is 5.1 x lO m. Substituting these values into the equation for B yields about 2.8 X 10 g/m for the burden. 

This is one source of acid rain, a serious environmental problem. The sulfur dioxide content of an air sample can be determined. A sample of air is bubbled through an aqueous solution of hydrogen peroxide to convert all of the SO2 to H2 SO4. H2 O2 + SO2 H2 SO4 Titration of the resulting solution completes the analysis (both H atoms of H2 SO4 are titrated). In one such case, the analysis of 1.55 X 10 Lof Los Angeles air gave a solution that required 5.70 mL of 5.96 X 10 M NaOH to complete the titration. Determine the number of grams of SO2 present in the air sample. 

As described in Chapter 5, sulfur dioxide, a by-product of burning fossil fuels, is the primary contributor to acid rain. Determine the Lewis stmcture of SO2. ... 

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. Natural (unpolluted) precipitation is naturally acidic with a pH often in the range of 5 to 6 caused by carbonic acid from dissolved carbon dioxide and sulfurous and sulfuric acids from natural emissions of SO and H2S. Human activity can reduce the pH very significantly down to the range 2 to 4 in extreme cases, mainly caused by emissions of oxides of sulfur. Because atmospheric pollution and clouds travel over long distances, acid rain is not a local problem. The problem may manifest itself a long way from the source. Problems associated with acid rain include ... 

Hydrogen sulfide is released primarily as a gas and will spread in the air. However, in some instances, it may be released in the liquid waste of an industrial facility. When hydrogen sulfide is released as a gas, it may form sulfur dioxide and sulfuric acid in the atmosphere. Sulfur dioxide can be further broken down and is a major contributor to acid rain. Hydrogen sulfide is estimated to remain in the atmosphere for an average of 18 hours. You will find more about what happens to hydrogen sulfide when it enters the environment in Chapters 4 and 5. 

FIGURE 44 Weathering. A weathered sandstone column. Calcite (composed of calcium carbonate) is dissolved by rain and groundwater (see Textbox 73). When stone in which calcite is a main component as, for example, sandstone, limestone, and marble, is in contact with water for long periods of time, it is weathered and partly or entirely dissolved. Pollutants such as sulfur dioxide are fundamental in accelerating the weathering and dissolution process. When sulfur dioxide, for example, dissolves in rainwater, it forms sulfuric acid, a strong acid that, at ambient temperatures, rapidly dissolves calcium carbonate. 

Sulfur Dioxide. Sulfur dioxide and nitrogen oxides, which are produced in modern society when coal, gas, and oil are burned in cars, power plants, and factories, react with water vapor in the air to form acids that negatively affect organic materials and even metals and stone when dissolved in airborne rainwater, the oxides of sulfur and nitrogen are the main cause of the formation of acid rain (see below). 

Schuster, P. F., M. M. Reddy, and S. I. Sherwood (1991), A quantitative field study of the role of acid rain and sulfur dioxide in marble dissolution, La Conservation des Monuments dans le Bassin Mediterranean, Proc. 2nd Int. Symp., Geneve. 

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