Acid Rain

Acid Rain, form of air pollution, currently a subject of great controversy because of the widespread environmental damage for which it has been blamed. It forms when oxides of sulphur and nitrogen combine with atmospheric moisture to yield sulphuric and nitric acids, which may then be carried long distances from their source before they are deposited by rain. The pollution may also take the form of snow or fog or be precipitated in dry forms. In fact, although the term “acid rain” has been in use for more than a century—it is derived from atmospheric studies that were made in the region of Manchester, England—the more accurate scientific term would be “acid deposition”. The dry form of such precipitation is just as damaging to the environment as the liquid form.

The problem of acid rain originated with the Industrial Revolution, and it has been growing ever since. The severity of its effects has long been recognized in local settings, as exemplified by the periods of acid smog in heavily industrialized areas. The widespread destructiveness of acid rain, however, has become evident only in recent decades. One large area that has been studied extensively is northern Europe, where acid rain has eroded structures, injured crops and forests, and threatened or depleted life in freshwater lakes. In 1984, for example, environmental reports indicated that almost half of the trees in Germany's Black Forest had been damaged by acid rain. The north-eastern United States and eastern Canada have also been particularly affected by this form of pollution; damage has also been detected in other areas of these countries and other regions of the world. In China, rapid industrial growth and an increasing demand for coal in the 1990s has led to a dramatic rise in environmental damage from acid rain. Nearly 40 per cent of China's land area is now affected, a figure scientists expect will continue to rise.

Industrial emissions have been blamed as the major cause of acid rain. Because the chemical reactions involved in the production of acid rain in the atmosphere are complex and as yet little understood, industries have tended to challenge such assessments and to stress the need for further studies; and because of the cost of pollution reduction, governments have tended to support this attitude. Studies released by the US government in the early 1980s, however, strongly implicated industries as the main source of acid rain, in the eastern United States and Canada. In 1988, as part of the United Nations Convention on Long-Range Transboundary Air Pollution Agreement (1979), 25 nations ratified a protocol freezing the rate of nitrogen oxides emissions at 1987 levels. The 1990 amendments to the US Clean Air Act of 1967 put in place regulations to reduce the release of sulphur dioxide from power plants by half to about 10 million tonnes per year by January 2000. A further reduction to 8.95 million tonnes was introduced in 2000 to be achieved by 2007, although it is not expected to be realized until 2010.

In Europe, the 1979 Convention is administered through the United Nations Economic Commission for Europe. The UNECE produced the first Sulphur Protocol (1985), which called for a reduction of sulphur emissions to 70 per cent of 1980 levels by 1993 (this was the only UNECE protocol not signed by the United Kingdom, although it nevertheless achieved the reduction, as did the 21 countries that did sign); the Nitrogen Oxides protocol (1988), which stipulated that total annual emissions of nitrogen oxides should not exceed 1987 levels by December 1994 (achieved by 17 of the 26 countries that signed the protocol as of 1996, including several significant reductions); the Volatile Organic Compounds Protocol (1991), which called for a reduction in emissions to 70 per cent of 1988 levels by 1999 (7 of the 17 countries that signed the protocol achieved their targets, including the UK, while most achieved considerable progress as of 2000); and the second Sulphur Protocol (1994), by which sulphur emissions are to be reduced in intermediate stages to a goal of 20 per cent of 1980 levels by 2010 (by 2000, 15 of the 20 countries that signed the protocol had attained the emission reductions required for that intermediate stage, while another 4 were on course to do so). In addition, catalytic converters, which reduce the emission of nitrogen oxides, have been compulsory on all new cars in the UK since 1993.

In October 1999 scientists from the Environmental Protection Agency in the United States claimed that lakes and streams across Europe and North America appeared to be recovering from the damage done by acid rain and that this recovery was mainly due to the stricter controls on industrial emissions of sulphur dioxide. The researchers warned, however, that it would still take decades before the widespread damage to forests, crops, and human health could be completely reversed. In 2001 the National Expert Group on Transboundary Air Pollution announced that the deposits from acid rain had halved in the UK over the previous two decades.