Nitrogen oxides, acid deposition

In addition to compounds of sulphur and nitrogen oxides, acid precipitation is known to contain a variety of heavy metals, particularly in the vicinity of metal smelters. The metals such as lead, cadmium, zinc and vanadium are obviously soluble, and in areas experiencing high rainfall are washed out, giving rise to rather higher levels of deposition than in low rainfall areas. 

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. 

Separate the copper and antimony by dissolving the deposit in a mixture of 5 mL concentrated nitric acid, 5 mL 40 per cent hydrofluoric acid (CARE), and 10 mL water boil off the nitrogen oxides, dilute to 150 mL, and add dropwise a solution of potassium dichromate until the liquid is distinctly yellow. Deposit the copper by electrolysing the solution at room temperature and limiting the cathode vs S.C.E. potential to —0.36 volt. Evaluate the weight of antimony by difference. 

Acid deposition has been known to exist since early in the industrial age. The principle pollutants responsible for the elevated levels of acidity are the oxidized forms of sulphur and nitrogen that have been emitted as by-products from non-ferrous smelters, fossil-fueled power generating stations, and motor vehicles. The pollutants are transported substantial distances from the source areas by the atmosphere. They are deposited on receptor regions remote from the sources as acidic rain, snow, and fog or as gasses and dry particulates. 

Demonstrations (see below) of the acidic properties of the oxides of nitrogen and sulfur show students some of the inorganic reactions that will be background for class discussions and homework assignments. The students are also expected to know the natural and industrial sources of each gas. They must also be reminded of chemistry topics they have already studied, such as gas behavior and equilibrium, that will provide relevant background for understanding acid deposition. 

Sulfur dioxide emissions in both Canada and the USA peaked in the early 1970s and have declined ever since with year-to-year variability. Actions to reduce acid deposition have been focused mainly on S02 emissions because they play generally a much higher role in rainfall acidification than nitrogen oxides. However, this is not the case in some areas of North America, like California, where nitrogen emissions are predominant and consequently contribute the major part in acidity as well. 

In accordance with the production plans (Odisharia et al 1994), the increase of emission rate for nitrogen oxides (NO ) in the area of Bovanenkovo gas exploration in Yamal peninsula will be during 2000-2015 (Figure 7). Emission of sulfur oxide will be practically permanent and will amount to about 470,000 tons per year. These data indicate also the growth of deposition rate for acid forming and eutrophication compounds in comparison with the present period (Table 1). 

Acid deposition acid rain a form of pollution depletion in which pollutants, such as nitrogen oxides and sulfur oxides, are transferred from the atmosphere to soil or water often referred to as atmospheric self-cleaning. The pollutants usually arise from the use of fossil fuels. 

Ammonia has a lifetime of only a few hours to a few days in the atmosphere. It and its reaction products are transported through the atmosphere and deposited on terrestrial snrfaces elsewhere. It is the main gaseous alkaline species in the atmosphere and neutralizes a large part of the acid produced in oxidation of sulfur and nitrogen oxides, probably up to a half though its dry-deposition is much faster than that of NO and SO2 (Dentener and Crutzen, 1994). Dry- and wet-deposition of ammonia contribute to soil acidification because 2 mol of H+ are produced in the nitrification of Imol of NH4+. Also a large part of the ammonia deposited on moist forest soils may be re-emitted as N2O (Section 8.2). 

Acid deposition or, acid rain, occurs when SO2 and oxides of nitrogen (NOx) react with water, oxygen, and oxidants to form acidic compounds. It is deposited in dry form (gas, particles) or wet form (rain, snow, fog), and can be carried by wind hundreds of miles across state and national borders. Acid rain harms lakes and streams, damages trees, crops, historic buildings, and monuments. 

Oxides of nitrogen also contribute to the formation of acid deposition. These oxides are formed whenever sufficient heat is generated in a power generating plant or industrial operation to allow the formation of nitric oxide from nitrogen and oxygen ... 

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. 

The environmental effects of acid deposition that have been most thoroughly studied are probably those on lakes, ponds, and other bodies of fresh water. When acid and oxides of sulfur and nitrogen are added to such bodies of water, the pH of the lake or pond tends... 

Oxides of nitrogen play a central role in essentially all facets of atmospheric chemistry. As we have seen, N02 is key to the formation of tropospheric ozone, contributing to acid deposition (some are toxic to humans and plants), and forming other atmospheric oxidants such as the nitrate radical. In addition, in the stratosphere their chemistry and that of halogens interact closely to control the chain length of ozone-destroying reactions. 

It is known from studies carried out over many decades that oxides of nitrogen at high concentrations dissolve in aqueous solution and react to form species such as nitrate and nitrite. With the focus on acid deposition and the chemistry leading to the formation of nitric and sulfuric acids during the 1970s and 1980s, a great deal of research was carried out on these reactions at much lower concentrations relevant to atmospheric conditions (for reviews, see Schwartz and White, 1981, 1983 and Schwartz, 1984). 

Historically, the major acids believed to contribute to acid deposition in the troposphere have been sulfuric and nitric acids, formed by the oxidation in air of S02 and oxides of nitrogen, respectively. However, there is an increasing recognition that organic acids may contribute significantly to the total acid burden and indeed may represent the major acidic species even in polluted urban environments. In addition, since nitrous acid (HONO) is formed whenever N02 and water are present (see Chapter 7.B.3), its contribution to the total acidity, particularly to indoor air environments, has become of interest and concern. 

Scientists have discovered that air pollution from the burning of fossil fuels is the major cause of acid rain. Acidic deposition, or acid ram, as it is commonly known, occurs when emissions of sulfur dioxide (SO ) and oxides of nitrogen (NOx) react in the atmosphere with water, oxygen, and oxidants to form various acidic compounds. This mixture forms a mild solution of sulfuric acid and nitric acid. Sunlight increases the rate of most of these reactions. 

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