Pollution, contamination of the environment by man-made substances or energy that haveadverse effects on living or non-living matter. This contamination of air, water, or soil materialsinterferes with human health, the quality of life, or the natural functioning of ecosystems. Insimple terms, pollution can be seen as the wrong substance in the wrong place in the wrongquantities at the wrong time. This implies that harm is caused to the environment, and if thesame substance is present at levels too low to cause harm, then it can be considered ascontamination. Many substances that can be pollutants also occur naturally, in which case theyare not classified as pollution. However, other pollutants result entirely from human activity,such as most toxic organic compounds and artificial forms of radioactivity, particularly fromnuclear waste
TYPES OF POLLUTION
Pollution can be categorized according to the medium in which it occurs: atmospheric pollution( see
Air Pollution), freshwater and sea pollution (see Water Pollution), or land pollution ( see
Solid Waste Disposal). However, transfers can occur in both directions between theatmosphere, water, and the land, with consequences for both the spread of pollution and itseffects. For example, the emission of sulphur dioxide—caused by the combustion of fossil fuelssuch as gas, petroleum, and coal—into the air can result in the acidification of soils and lakeswhen it reaches the Earth’s surface (see Acid Rain). Pollution can also be classified on the basisof the type of pollutant, such as pesticides ( see
Pest Control) and other persistent toxic organiccompounds, heavy metals, radioactivity, human and animal effluent, and toxic gases. Themost familiar forms of pollution result from the chemical properties of the substancesconcerned, but the physical properties may also be important, for example ionizing radiation,noise pollution, and excessive heat.Water pollution arises from the discharge of industrial, agricultural, and human wastes intofreshwaters, estuaries, and seas. This may result in the poisoning of aquatic organisms or thedepletion of oxygen owing to excessive growth of micro-organisms (anthropogeniceutrophication), which makes less of the water habitable for fish. Metal pollution and toxicorganic compounds are of concern for human and environmental health as a result of discharges to water, air, and the terrestrial environment. Air pollution can result in adverseeffects on health, crops, natural ecosystems, materials, and visibility. The major concerns over air pollution are acidification of soils and waters with its detrimental affects on animal andplant life, and the impact of traffic-derived pollutants on health in cities (see Traffic Pollution).On a global scale air pollution probably represents the greatest problem of all, with greenhousegases (such as carbon dioxide) resulting in global warming and synthetic chlorine compounds(chlorofluorocarbons) depleting the stratospheric ozone layer. Nuclear waste is a furthermodern environmental concern, which poses a problem not just for the present generation, butfor future generations as the waste remains radioactive for thousands of years
TRENDS IN POLLUTION
Trends in pollution are difficult to determine accurately, particularly on a world scale. The best-documented trend is the global increase in carbon dioxide at a rate of about 0.5 per cent peryear. Overall, there is a trend for decreasing levels of pollutants in the developed world, butthe opposite in many developing countries as they rapidly industrialize. For example, it hasbeen predicted that sulphur dioxide emissions will fall by 63 per cent in Europe from 1990 to2010, while they will rise in China by 118 per cent. The reductions in the developed worldresult largely from environmental legislation, which has led to the introduction of controlmeasures and cleaner technology. Examples are the introduction of more advanced waste-water treatment processes, shifts to cleaner fuels, and the recycling of potential contaminants
Air Pollution, contamination of the atmosphere by gaseous, liquid, or solid wastes or by-products that can endanger human health and the health and welfare of plants and animals, orcan attack materials, reduce visibility, or produce undesirable odours. Among air pollutantsemitted by natural sources, only the radioactive gas radon is recognized as a widespreadmajor health threat, although gases and particles from volcanic eruptions can cause seriousmore localized problems. A by-product of the radioactive decay of uranium minerals in certainkinds of rock, radon seeps into the basements of homes built on these rocks, posing a risk of lung cancer to residents.Each year industrially developed countries generate billions of tons of pollutants. The mostprevalent and widely dispersed air pollutants are described in the accompanying table. Thelevel is usually given in terms of atmospheric concentrations (micrograms of pollutants percubic metre of air) or, for gases, in terms of parts per million, that is, millilitres of gas perthousand litres of air. Many come from directly identifiable sources; sulphur dioxide, forexample, comes from electric power plants burning coal or oil. Others are formed through theaction of sunlight on previously emitted reactive materials (called precursors). For example ozone, a dangerous pollutant in smog, is produced by the interaction of hydrocarbons andnitrogen oxides under the influence of sunlight. Ozone also causes serious crop damage. Onthe other hand, the discovery in the 1980s that air pollutants such as fluorocarbons arecausing a loss of ozone from the Earth's protective ozone layer has caused the phasing out of these materials. A further category of air pollution is heavy metals, present as particulates andarising from many industrial processes.
METEOROLOGY AND HEALTH EFFECTS
Pollutant concentration is reduced by atmospheric mixing, which depends on such weatherconditions as temperature, wind speed, and the movement of high and low pressure systemsand 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 pollutantsmay accumulate near the ground. Inversions can become sustained under a stationary high-pressure system coupled with low wind speeds.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 injuryand even death. An inversion over Donora, Pennsylvania, in 1948 caused respiratory illness inover 6,000 people and led to the deaths of 20. Severe pollution in London took 3,500 to 4,000lives in 1952 and another 700 in 1962. Release of methyl isocyanate into the air during atemperature inversion caused the disaster at Bhopal, India, in December 1984, with at least3,300 deaths and more than 20,000 illnesses. The effects of long-term exposure to lowconcentrations are not well defined; however, those most at risk are the very young, theelderly, smokers, workers whose jobs expose them to toxic materials, and people with heart orlung disease. Other adverse effects of air pollution are injury to livestock and crops.Often, the first noticeable effects of pollution are aesthetic and may not necessarily bedangerous. These include visibility reduction due to tiny particles suspended in air, or badodours, such as the rotten egg smell produced by hydrogen sulphide emanating from pulp andpaper mills.
SOURCES AND CONTROL
The combustion of coal, oil, and petrol accounts for much of the airborne pollutants. About 60per cent of the sulphur dioxide and 20 per cent of the nitrogen oxides emitted into theatmosphere 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 fromburning petrol and diesel in cars and lorries. Other major pollution sources include iron andsteel mills; smelters; municipal incinerators; oil refineries; cement plants; and nitric andsulphuric 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. Carbonmonoxide, for example, is a typical product of internal-combustion engines. Methods forcontrolling air pollution include removing the hazardous material before it is used, removingthe pollutant after it is formed, or altering the process so that the pollutant is not formed oroccurs only at very low levels. Car exhaust pollutants can be controlled by burning the fuel ascompletely as possible, by recirculating fumes from fuel tank, carburettor, and crankcase, andby changing the engine exhaust to harmless substances in catalytic converters. Industriallyemitted particulates may be trapped in cyclones, electrostatic precipitators, and filters.Pollutant gases can be collected in liquids or on solids, or incinerated into harmlesssubstances
The tall smokestacks used by industries and utilities do not remove pollutants but simply boostthem higher into the atmosphere, thereby reducing their concentration at the site. Thesepollutants may then be transported over large distances and produce adverse effects in areasfar from the site of the original emission. Sulphur dioxide and nitrogen oxide emissions fromBritain and other industrialized countries of Western and Central Europe have caused acid rainin Norway and Sweden. The pH level, or relative acidity, of many freshwater lakes has beenaltered so dramatically by acid rain that entire fish populations have been destroyed. Sulphurdioxide emissions and the subsequent formation of sulphuric acid can also be responsible forthe attack on limestone and marble at large distances from the source. he 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 allowssolar energy to enter the atmosphere but reduces the reemission of infrared radiation from theEarth, may well lead to a warming trend that might affect the global climate and lead to apartial melting of the polar ice-caps. Possibly an increase in cloud cover or absorption of excesscarbon dioxide by the oceans (in the so-called carbon cycle) would check the greenhouseeffect before it reached the stage of polar melting. Nevertheless, many research reportsreleased during the 1990s have indicated that the greenhouse effect is definitely under wayand that the nations of the world should be taking immediate steps to deal with it. In June 1999a massive cloud of air pollution, roughly the size of the United States, was discovered 1 km to3 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 sulphurdioxide. Scientists believe it was created by human activities, especially the burning of fossilfuels, and could have a significant impact on the regional and global climate, as well as plantand animal life V
ACTION BY GOVERNMENTS
Various countries have set standards in legislation in the form of concentration levels that arebelieved to be low enough to protect public health. Source emission standards are alsospecified to limit the discharge of pollutants into the air so that air-quality standards will beachieved. However, the nature of the problem requires the implementation of international nvironmental treaties, and to this end 49 countries agreed in March 1985 on a United Nationsconvention to protect the ozone layer. This “Montreal Protocol”, which was renegotiated in1990 and 1992, called for the phaseout of certain chlorocarbons and fluorocarbons by the endof the century and provides aid to developing countries in making this transition. In addition,several international protocols have been aimed specifically at reducing the incidence of acidrain. In December 1999 the Montreal Protocol announced that almost all production andconsumption of virgin ozone depleting substances had been phased out in the developedworld. Similar control measures were introduced for developing countries in July 1999, and itwas anticipated that all developing countries would be able to meet their freeze targets andsubsequent obligations under the protocol.Concern over trans-boundary air pollution, including acid rain, in Europe has led to the UnitedNations Economic Commission for Europe (UNECE) developing air quality guidelines, calledCritical Loads and Levels, which represent thresholds below which it is believed that damagewill not occur to different ecological systems. Critical Loads are based on the amount of aciditythat an ecosystem can tolerate being deposited indefinitely. Critical Levels are concentrationsof ozone, sulphur dioxide, and nitrogen oxides over different averaging times and applicable todifferent categories of vegetation. Massive cuts are being made in emissions in Europe in orderto move towards these thresholds. In contrast, in many developing countries, pollutantconcentrations are rising very rapidly due to increased industrialization and motor traffic;concern in such places is primarily with impacts on human health in cities. The World HealthOrganization has published air quality guidelines designed to protect health