Air pollution is the result of the discharge into the atmosphere of foreign gases, vapours, droplets and particles, or of excessive amounts of normal constituents, such as the carbon dioxide and suspended particulate matter produced by the burning of fossil fuels. A growing body of evidence seems to show a consistent association between air pollution and health impairment of varying degrees. Such associations are found between acute pollution exposure and morbidity and mortality; chronic lower-level exposure and morbidity and mortality; exposure and impairment of function and performance; exposure and symptoms of sensory irritation; and exposure and other effects on well-being.
A relatively new feature of the effects of air pollutants is the association with long term global problems. Considerable uncertainty surrounds scenarios relating to the effect of increased levels of carbon dioxide, but some predictions are of major impact on climate. The most significant polluting substances are sulphur dioxide and the oxides of nitrogen produced by power stations burning coal or oil and motor cars. The phenomenon of acid deposition is widespread throughout northern temperate regions, and researchers have associated 'acid rain' with damage to wildlife and wildlife habitats, including freshwaters and forests. Both wet and dry acid deposition is associated with damage to artefacts and materials. More locally, environmental contamination has resulted from long-term use of materials such as asbestos and lead, whose full impact as air pollutants has emerged only recently.
Airborne toxic agents, including micro-organisms and other harmful agents such as respirable dust, may have long-term effects such as genetic damage, carcinogenesis, and shortened life expectancy. The effect on an individual of foreign substances in the ambient environment depends on his health and on the degree and duration of exposure. Symptoms may not be readily distinguishable and their medical assessment is not always easy. Practical difficulties also arise from the inadequacy of long-term sampling procedures and analytical techniques.
The recommendation of maximum permissible limits for international adoption is a complicated procedure. Countries vary greatly in the amount of airborne known toxic and harmful agents workers may be exposed to so that one country may allow exposure to a toxic agent to be up to 90 times greater than the exposure permitted in another country. Permissible limits are normally based on an exposure of eight hours a day for five days a week. Different considerations must apply when people are exposed briefly to high concentrations, when working periods are longer than normal, or when workers are subjected to additional stresses such as high temperatures or poor nutrition.
WHO estimates that about 1.6 billion people worldwide (over 20% of the population) are exposed to air that is polluted (contaminated above international safety limits). Another study, by Cornell University, estimated that worldwide air pollution harms the health of four to five billion people a year, more than two-thirds of the global population.
Children, who breathe in twice as much air as adults (proportionate to body weight), are the most vulnerable of all.
Mexico City, the world's most populous and polluted city, has oxygen booths in local parks and malls for breathing relief. Dust, lead and chemicals made the city's air unsafe to breathe for 302 days in 1990.
Many people in the USA live in areas which fail to meet federal air quality standards. The Environmental Protection Agency (EPA) estimates that over 125 million Americans breathe unhealthy air--almost half of the US population. Heart and lung disease aggravated by air pollutants results in as many as 64,000 premature deaths a year -- more than die from car accidents each year. The dimension of the problem is indicated by the fact that industry in the USA in 1989 spend $33 billion on clean air, more per capita than any of its trading partners. Further proposals suggest the need to increase that amount by $25 billion. Air pollution in the USA is estimated to cause up to 50,000 deaths per year and to cost $40 billion in health care and lost work days.
There is a major difference between air pollution trends in developed and developing countries. Strenuous efforts have begun to abate atmospheric pollution in many industrialized countries but urban air pollution is reaching crisis dimensions in most large cities of the developing world. Road traffic, the burning of coal and high-sulphur fuels, and forest fires are the major causes of air pollution. People in developing countries are also exposed to high levels of indoor pollutants from open fires. Some 50 per cent of chronic respiratory illness is now thought to be associated with air pollution.
Atmospheric pollution is a relatively minor problem in the African and West Asian regions. In Africa, there are problems in the urbanized and industrialized areas in the north and south, for example from vehicles, which are often old and use leaded fuel, and from some manufacturing, mining and industrial activities and power stations. Biomass burning is an additional problem in Africa. If the projected demand for transport and electricity in Africa is met with current technologies, emissions from vehicles will rise fivefold and from power stations elevenfold by 2003 (World Bank 1992). In West Asia, air pollution is a problem mainly in the larger cities, exacerbated by the high temperatures and levels of sunlight.
The Asian and Pacific region has experienced significant growth in atmospheric pollution, resulting from the heavy use of coal and high sulphur fuels, traffic growth and forest fires. The most serious problems are in urban areas and the developing countries in the region. Japan, however, has reduced sulphur emissions through gains in efficiency, heavier reliance on oil and nuclear power, and stringent pollution control laws.