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Acid Rain 1970 1985 • Our atmosphere contains many pollutants from human activities. Some of these come from fossil fuels, which release large amounts of sulphur dioxide (SO2) and nitrogen oxides (NOX) into the air. Combined with water and powerful oxidants like ozone, sulphur and nitrogen oxides become sulphuric and nitric acid. These acids may travel long distances before falling to the earth as rain, snow, sleet, hail, fog, dew or dust. Effect of acidic precipitation on aquatic ecosystems • Most biological life thrives best within a narrow range of pH levels, near neutral or 7.0. Aquatic vegetation and animal life vary in their susceptibility to changes in pH; some species are more acid-tolerant than others. Aquatic systems that are well-buffered may not be as affected by acidic runoff as those that lack a buffering capacity. In lakes and streams whose waters become acidified, micro-organisms may be affected. As organisms lower in the food chain are reduced, species higher up the food chain that rely on these organisms for food will be affected. Plankton and invertebrates are most sensitive to changes in pH. If the pH levels drop below 5.0 most fish species are affected. Effect of acidic precipitation on soils and plant growth • Some plants are tolerant of acidic conditions, while others are not. Acidic soils may affect micro-organisms in the soil, which play important roles in plant growth. Acidity affects the availability of nutrients that are essential for plant growth and increases leaching of aluminium and mercury, which are toxic to plants at high levels. Nitrogen is a nutrient and at certain levels, nitrogen deposition from air emissions has increased growth of vegetation; however, at higher levels, excess nutrients can reduce plant growth. Effect of acid rain on buildings and materials • Acidic precipitation is corrosive of metals and alkaline building materials such as marble and limestone. Urban areas subject to high levels of exhaust fumes and other sources of acidic precipitation have experienced significant weathering of statues and building materials • in Germany's "Black Forest" or "Schwarzwald," more than 50% of the forest has been severely damaged by acid rain. Many trees have dried out and died already, while many others have discoloured leaves. Even tree planting has failed to halt this destruction, since the soil is already acidic. Ironically, countries like Sweden, Norway, and other Scandinavian countries do not contribute much to atmospheric pollution, but they are suffering extensive damage from atmospheric pollutants carried there from other countries. For example, it has been reported that fish have disappeared from one-third of the lakes and marshes of Norway. The origin of the deposition of sulphur (left) and oxidized nitrogen (right) over Germany (above) and Sweden (below) in 2003. Legislative controls • The UK, as a member country of the European Union, is under obligation to comply with the Large Combustion Plant Directive of 1988 which concerns reductions in emissions of SO2 and NOx from plants over 50MW in size • The UK is, under this Directive, required to reduce SO2 by 60% by 2003 and NOx by 30% by 1998 (from 1980 levels). • The UK is also a Party to the Gothenburg Protocol, designed to Abate Acidification, Eutrophication and Ground-level Ozone. The UK is committed to reducing 1990 emissions of sulphur dioxide by 75% by 2010 and nitrogen oxides by 50% over the same period. In addition, the UK National Air Quality Strategy sets out standards and objectives for reducing key air pollutants to be achieved by year 2005. To meet the objectives for the acid deposition pollutants (largely SO2 and NOx), industry will have a significant part to play in reducing emissions. • As most of the SO2 emitted in the UK is from industry and power generation, reductions in annual emissions will be necessary from industrial sources. The use of cleaner fuels and the use of control technologies will be required at all new industrial plants if SO2 levels are to continue in a downward trend. Contribution to UK Total UK emissions 1999 emissions million tonnes from road transport Nitrogen Oxides 44% 1.6 (NOx) Carbon Monoxide 69% 4.8 (CO) Hydrocarbons 27% 1.7 (VOCs) Black Smoke 48% 0.3 Vehicle pollution can be significantly reduced by fitting a catalytic converter to the exhaust system. This is a relatively low cost method of pollution control (around £350) which has little effect on vehicle performance and fuel consumption. All new cars sold in Britain from January 1993 onwards have catalytic converters • In 1988 a Directive was introduced for European Community (EC) countries which required power stations to reduce emissions of sulphur dioxide and nitrogen oxides. This was helped through new gas- fired power stations (which have lower emissions) replacing coal fired power stations, and flue gas desulphurisation equipment fitted to some of the existing coal-fired power stations.
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