Acid Rain is a rain containing a high level of acidity. The term is also commonly used to refer to other forms of precipitation contaminated by acid ad to acidic s\dust particles that fall to the ground. Acid rain results chiefly from chemical reactions involving two types of air pollutants: oxides of sulfur and nitrogen. In the atmosphere, these gases change into substances that, when combined with water, yield sulfuric or nitric acid. Among the major sources of sulfur and nitrogen oxide emissions are power plants, motor vehicles, and smelting furnaces.
Acid rain can cause the water in lakes and streams to become acidic, killing off fish and other aquatic life. It may also damage forests and lead to the deterioration of paint and of exposed metal and stone surfaces (see Alm, Leslie R. Regional Influences and Environmental Policymaking: A Study of Acid Rain). Among the areas with the most severe acid rain are the eastern part of the North America and the northern and central parts of Europe.
This paper investigates what acid rain really is and how it affects to us and to our nature.
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 (see Geyh, Alison S. Nitrous Acid, Nitrogen Dioxide and Ozone Concentrations in Residential Environments).
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 (see Davidson, Joan. How Green is your City? Pioneering Approaches to Environmental Action). 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 (see Acid Rain Still a Major Problem. Western Mail. July 15, 2004).
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) (see Acid Rain. The Columbia Encyclopedia, Sixth Edition. Columbia University Press, New York, 2004). 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 (see Johnston, R. J. Environmental Problems: Nature, Economy and State. London: Belhaven, 1999).
A. Air Pollution and Acid Rain
Rainwater was once the purest form of water available but now is often contaminated by pollutants in the air. Acid rain is caused when industrial emissions mix with atmospheric moisture. Pollutants may be carried in clouds for long distances before falling, which mean that forests and lakes far away from factories may be damaged by acid rain. In the near vicinity of the factories, additional damage is caused by the deposition of larger pollutant particles falling to the ground in dry form. Air pollution has been increasing since the Industrial Revolution but only recently have side effects such as acid rain become severe and widespread enough to evoke international concern (see Pollution Allowance. The Columbia Encyclopedia, Sixth Edition. Columbia University Press, New York, 2004).
Each year industrially developed countries generate billions of tons of pollutants. The most prevalent and widely dispersed air pollutants are described in the accompanying table. The level is usually given in terms of atmospheric concentrations (micrograms of pollutants per cubic meter of air) or, for gases, in terms of parts per million, that is, milliliters of gas per thousand liters of air. Many come from directly identifiable sources; sulphur dioxide, for example, comes from electric power plants burning coal or oil. Others are formed through the action of sunlight on previously emitted reactive materials (called precursors).
For example, ozone, a dangerous pollutant in smog, is produced by the interaction of hydrocarbons and nitrogen oxides under the influence of sunlight. Ozone also causes serious crop damage. On the other hand, the discovery in the 1980s that air pollutants such as fluorocarbons are causing a loss of ozone from the Earth’s protective ozone layer has caused the phasing out of these materials (see Baird, Stephen L. Creating a Star: The Science of Fusion Fusion Power Would Not Contribute to Global Warming, Acid Rain, or Other Forms of Air Pollution, nor Would It Create Long-Lived Radioactive Waste). A further category of air pollution is heavy metals, present as particulates and arising from many industrial processes.
B. Meteorology and Health Effects
Pollutant concentration is reduced by atmospheric mixing, which depends on such weather conditions as temperature, wind speed, and the movement of high and low pressure systems and their interaction with the local topography, for example, mountains and valleys. Normally, temperature decreases with altitude. But when a colder layer of air settles under a warm layer, producing a temperature or thermal inversion, atmospheric mixing is retarded and pollutants may accumulate near the ground. Inversions can become sustained under a stationary high-pressure system coupled with low wind speeds (see Environment Matters: Industry’s Guide to the Issues, the Challenges and the Solutions).
Periods of only three days of poor atmospheric mixing can lead to high concentrations of hazardous materials in high-pollution areas and, under severe conditions, can result in injury and even death. An inversion over Donora, Pennsylvania, in 1948 caused respiratory illness in over 6,000 people and led to the deaths of 20. Severe pollution in London took 3,500 to 4,000 lives in 1952 and another 700 in 1962. Release of methyl isocyanate into the air during a temperature inversion caused the disaster at Bhopal, India, in December 1984, with at least 3,300 deaths and more than 20,000 illnesses.
The effects of long-term exposure to low concentrations are not well defined; however, those most at risk are the very young, the elderly, smokers, workers whose jobs expose them to toxic materials, and people with heart or lung disease. Other adverse effects of air pollution are injury to livestock and crops (see Magraw, Daniel Barstow. International Law and Pollution. University of Pennsylvania Press. 2004).
Often, the first noticeable effects of pollution are aesthetic and may not necessarily be dangerous. These include visibility reduction due to tiny particles suspended in air, or bad odors, such as the rotten egg smell produced by hydrogen sulphide emanating from pulp and paper mills.
C. Sources and Control
The combustion of coal, oil, and petrol accounts for much of the airborne pollutants. About 60 per cent of the sulphur dioxide and 20 per cent of the nitrogen oxides emitted into the atmosphere in the United Kingdom are produced by fossil-fuel-fired electric power plants. About 70 per cent of the carbon monoxide and 50 per cent of the nitrogen oxides come from burning petrol and diesel in cars and lorries. Other major pollution sources include iron and steel mills; smelters; municipal incinerators; oil refineries; cement plants; and nitric and sulphuric acid plants.
Potential pollutants may exist in the materials entering a chemical or combustion process (such as sulphur in coal), or they may be produced as a result of the process itself. Carbon monoxide, for example, is a typical product of internal-combustion engines. Methods for controlling air pollution include removing the hazardous material before it is used, removing the pollutant after it is formed, or altering the process so that the pollutant is not formed or occurs only at very low levels (see Schneider, Conrad G. Every Breath You Take: Significant Reductions in Power Plant Emissions Will Be Necessary before We Can Clean Up America’s Air).
Car exhaust pollutants can be controlled by burning the fuel as completely as possible, by recirculating fumes from fuel tank, carburettor, and crankcase, and by changing the engine exhaust to harmless substances in catalytic converters. Industrially emitted particulates may be trapped in cyclones, electrostatic precipitators, and filters. Pollutant gases can be collected in liquids or on solids, or incinerated into harmless substances.
D. Large-Scale Effects
The tall smokestacks used by industries and utilities do not remove pollutants but simply boost them higher into the atmosphere, thereby reducing their concentration at the site. These pollutants may then be transported over large distances and produce adverse effects in areas far from the site of the original emission. Sulphur dioxide and nitrogen oxide emissions from Britain and other industrialized countries of Western and Central Europe have caused acid rain in Norway and Sweden.
The pH level, or relative acidity, of many freshwater lakes has been altered so dramatically by acid rain that entire fish populations have been destroyed. Sulphur dioxide emissions and the subsequent formation of sulphuric acid can also be responsible for the attack on limestone and marble at large distances from the source. There are also claims that acid rain has caused widespread damage to forests in Europe, but the precise role is unclear and earlier predictions of large-scale forest death are unfounded (see Jenner, Paul, and Smith, Christine. The Environmental Business Handbook. London: Euromonitor, 2003).
The worldwide increase in the burning of coal and oil since the late 1940s has led to ever-increasing concentrations of carbon dioxide. The resulting “greenhouse effect”, which allows solar energy to enter the atmosphere but reduces the reemission of infrared radiation from the Earth, may well lead to a warming trend that might affect the global climate and lead to a partial melting of the polar ice-caps.
Possibly an increase in cloud cover or absorption of excess carbon dioxide by the oceans (in the so-called carbon cycle) would check the greenhouse effect before it reached the stage of polar melting. Nevertheless, many research reports released during the 1990s have indicated that the greenhouse effect is definitely under way and that the nations of the world should be taking immediate steps to deal with it. In June 1999 a massive cloud of air pollution, roughly the size of the United States, was discovered 1 km to 3 km (’ mi to 2 mi) above the Indian Ocean.
The thick brown haze included soot, sulphates, nitrates, mineral dust, and significant amounts of gases such as carbon monoxide and sulphur dioxide. Scientists believe it was created by human activities, especially the burning of fossil fuels, and could have a significant impact on the regional and global climate, as well as plant and animal life (see Cristol, Hope. New Concern about Acid Rain: Trees’ Immune Systems May Be Damaged by Pollution).
E. Acid Deposition
Also associated with the burning of fossil fuels is acid deposition, which is caused by the emission of sulphur dioxide and nitrous oxides into the air from power plants and motor vehicles. These chemicals interact with sunlight, moisture, and oxidants to produce sulphuric and nitric acids, which are carried with the atmospheric circulation and come to Earth in rainfall and snowfall, commonly referred to as acid rain, and as dry deposits in the form of dry particles and atmospheric gases.
Acid rain is a localized problem. The acidity of some precipitation in northern North America and Europe is equivalent to that of vinegar. Acid rain corrodes metals, weathers stone buildings and monuments, injures and kills vegetation, and acidifies lakes, streams, and soils, especially in the poorly buffered regions of north-eastern North America and northern Europe. In these regions, lake acidification has killed some fish populations. It is also now a problem in the south-eastern and western United States (see Norman, Mille. Rains of Terror. Geographical. Volume: 72. Issue: 5, Page 90, 2002). Acid rain can also slow forest growth, and forest die-back has been major problem. It is associated with forest decline at high elevations in both North America and Europe.
Many fossil fuels, such as oil and coal, contain small amounts of sulphur. When they are burnt the sulphur can combine with oxygen from the air to form a choking gas called sulphur dioxide. Sulphur dioxide then dissolves in atmospheric moisture to form sulphurous acid. Rainwater polluted with this acid can dissolve the stonework of buildings and harm plants and trees. Environmental chemists studying such acid rain have worked out that damage to trees in Scandinavia is largely due to acid rain formed from sulphur dioxide released in industrial areas in northern England and southern Scotland, and carried across the North Sea by strong winds (see Simpson, Struan. The Times Guide to the Environment: a Comprehensive Handbook to Green Issues).
a) Marshy Spruce Forest Damaged by Acid Rain
Forests, lakes, ponds, and other terrestrial and aquatic environments throughout the world are being severely damaged by the effects of acid rain. Acid rain is caused by the combination of sulphur dioxide and nitrogen compounds with water in the atmosphere to produce rain with a very low pH. Normally, rainwater has a pH of 6.5, making it very slightly acidic. However, with the addition of sulphur and nitrogen compounds, the pH of rainwater may drop to as low as 2.0 or 3.0, similar to the acidity of vinegar (see Norman, Mille. Rains of Terror. Geographical. Volume: 72. Issue: 5, Page 90, 2002). In addition to chemically burning the leaves of plants, acid rain poisons lake water, which kills most if not all of the aquatic inhabitants.
G. Environmental Concerns
Acid rain, which damages buildings, soils, forests, fish, and other wildlife, is one of the major environmental issues facing Finland. The country’s emissions fell steadily in the late 20th century after the implementation of the United Nations (UN) Economic Commission for Europe (ECE) Sulphur Protocols, but Finland continues to receive sulphur dioxide and other acid-rain-causing pollutants from beyond its borders.
Air quality in Finland is generally better than in many other European countries, although substantial problems do exist as a result of emissions from motor vehicles and industrial sources. The vast majority of the population—and, consequently, the sources of air pollution—is concentrated in urban areas in the south-west part of the country (see Silber, Kenneth. Blowing Their Stacks over Pollution Rights. Insight on the News).
In Finland, it protects 6 per cent (1997) of its total land area in parks and other reserves—less than most other western European countries. Forest covers 66 per cent (1995) of the country, however, making Finland the most densely forested European country. The government has long played a role in regulating the timber industry to maintain the country’s valuable forest resources, and Finland sustains a remarkably low rate of deforestation—just 0.1 per cent (1990-1996) each year.
With more than 60,000 lakes, Finland has a large proportion of wetlands, which provide critical habitat for many bird and animal species. During the 20th century these wetlands diminished considerably, due in part to peat mining and to draining for agriculture (see Allaby, Michael. Basics of Environmental Science. Routledge. London, 2000). Most of Finland’s lakes are shallow, making them particularly susceptible to damage from acid rain.
While in Sweden, One of its major environmental problems is acid rain, which degrades soil, damages buildings, acidifies waterways, and defoliates forests. The country has made great strides in reducing sources of acid rain within its own borders—Sweden has an ambitious environmental protection programme and was among the first countries to introduce a carbon tax. Sweden emits 6.1 (1996) metric tons of carbon dioxide per capita, compared with 15.3 metric tons in Norway and 11.5 metric tons in Finland.
Sweden also has a sulphur tax and has cut its sulphur dioxide emissions by more than two-thirds since the early 1970s. Most of the air pollution that results in acid rain in Sweden, however, originates from emissions abroad. Acid levels in the country’s soil continue to rise as a result of pollution from other countries. Nitrogen run-off from farms in Sweden has caused severe pollution and eutrophication, or build-up of nutrients, in the North Sea and the Baltic Sea, as well as in many of the country’s lakes. As a result of eutrophication, algae growth has increased and animal life has declined (see Farmer, Andrew. Managing Environmental Pollution. Routledge. London, 2002).In 1988 a viral outbreak attributed to pollution killed nearly 65 per cent of the local seal population.
Another problem is soil degradation. Some soils are naturally acidic but may become more acidic due to acid rain or dry deposition of acid gases and particles. Acid rain has a pH of less than 5.6. The main sources of acidity in the atmosphere are the increasing quantities of sulphur dioxide and nitrogen oxides emitted by the combustion of fossil fuel.