Acid pollution is one of the major long-term environmental costs of the agricultural and industrial revolutions. The burning of coal, oil or natural gas by power plants, industry and road vehicles - combined with agricultural intensification - produces several primary pollutants such as sulphur dioxide (SO2), nitrogen oxides (NOx) and ammonia, which undergo chemical reactions that can produce secondary pollutants such as nitrogen dioxide (NO2, formed mainly by a reaction between nitric oxide (NO) and oxygen). These primary and secondary pollutants can be converted in the atmosphere, on the surface of buildings, inside plants, animals and humans, or below ground, into sulphuric and nitric acids.
Depending on a variety of biological, chemical and meteorological factors, soils, forests, lakes, rivers, animals, plants and buildings are susceptible in varying degrees to the effects of these pollutants, acting alone or in conjunction with other factors. Several of these pollutants also contribute to other environmental problems: nitrogen oxides, for example, are an ingredient in the creation of ground-level ozone (which is harmful to human health) and in threats to the ozone layer, and also contribute to eutrophication - the harmful build-up of nutrients and organic material in lakes (for more details, see McCormick, 1997).
The first signs of a link between the burning of fossil fuels and acidification were identified in Europe and North America in the mid-19th century, but there was to be no significant scientific or political response until the mid-20th century, when postwar economic reconstruction and expansion led to a doubling of demand for fossil fuels in Europe and North America, and new levels of consumption in Asia and Latin America. The world now relies on fossil fuels for 90 per cent of its commercial energy supplies: oil 41 per cent, coal 28 per cent, and natural gas 21 per cent, with the balance coming from nuclear power, hydropower and other sources.
As consumption increased, so pollutive emissions grew and acidification worsened. Accelerated research following the Second World War confirmed the existence of a problem with local, national and international dimensions, with the greatest emissions coming from the industrial centres of Europe and North America, and the most serious damage occurring downwind of those centres. The major chemical elements in the problem are as follows:
• Sulphur dioxide, produced mainly by power stations and other industrial plants which use fossil fuels, and by metal smelters, oil refineries and district heating installations. As noted in Chapter 7, power stations and refineries account for more than half of SO2 emissions in the EU, with the worst pollution coming from a relatively small number of point sources, mainly power stations. The 100 biggest emitters (one-third of them in western Europe) between them accounted for 42 per cent of European SO2 emissions in 1994, with the ten biggest alone accounting for more than two million tonnes of SO2 emissions each year (Barrett and Protheroe, 1994).
• Nitrogen oxides, for which road vehicles are the major source in Europe; they account for 63 per cent of EU emissions, while power stations account for just 20 per cent of emissions. The role of road traffic in the problem continues to grow as the numbers of vehicles on European roads grow.
• Volatile organic compounds (VOCs) are produced mainly by road vehicles, the chemical and petroleum industries, paints and glues, and the use of solvents in industrial processes. The United Nations defines VOCs as 'all organic compounds of anthroprogenic nature other than methane that are capable of producing photochemical oxidants by reaction with nitrogen oxides in sunlight'. This definition is so broad as to make it difficult to measure emissions and to identify trends in the production of VOCs.
• Ammonia (NH3), a byproduct of animal waste and fertilizer use, and a problem mainly in regions using intensive agricultural techniques. Calculating emissions is difficult since they depend on a variety of different factors, such as the nitrogen content of animal feed and the conditions under which wastes are spread. Nevertheless, UN figures suggest that Europe produces about 800000 tonnes of NH3 emissions every year (European Commission, 1995), hence it is now being taken more seriously by EU policymakers as an element in the broader problem of acidification. (This contrasts with the situation in the United States, where ammonia has so far drawn little attention in discussions about acid pollution.)
Debates about policy responses to acidification have been troubled consistently by the fact that different pollutants contribute at different levels to the overall problem of acidification from one region to another, depending on a variety of factors including the buffering capacity of soils, the distribution of emissions, local or regional climatic and weather conditions, and the neutralizing capacity of other chemicals. The Dobris Assessment concluded that sulphur was the dominant factor in central and eastern Europe while NOx 'may be relatively more important' in western and southern Europe. Meanwhile, ammonia 'makes a significant contribution' in those countries with intensive cattle breeding programmes, such as Denmark, the Netherlands and parts of Britain (Stanners and Bourdeau, 1995, p. 36).
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