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Air pollution and air quality

The World Health Organization (WHO) lists six 'classic' air pollutants: CO, lead, nitrogen dioxide (NO2), suspended particulate matter (SPM) - including dust, fumes, mists and smoke - SO2 and tropospheric ozone (O3) (WHO 1999).

The burning of fossil fuels and biomass is the most significant source of air pollutants such as SO2, CO, certain nitrous oxides such as NO and NO2 (known collectively as NOx), SPM, volatile organic compounds (VOCs) and some heavy metals. It is also the major anthropogenic source of carbon dioxide (CO2), one of the important greenhouse gases. Between 1973 and 1998, total energy supply increased by 57 per cent (see graph opposite), the majority provided by oil, natural gas and coal with nuclear and hydropower and other renewable resources playing a minor role (IEA 2000). The fuels used vary from region to region - for example, natural gas dominates in the Russian Federation, while coal provides 73 per cent of the energy consumed in China (BP Amoco 2000). Biomass is an important source of energy in the developing world and is the main source of indoor air pollution in such countries (Holdren and Smith 2000).

Acid precipitation has been one of the most important environmental concerns over the past decades especially in Europe and North America (Rodhe and others 1995), and more recently also in China (Seip and others 1999). Significant damage to forests in Europe became a high priority environmental issue around 1980, while thousands of lakes in Scandinavia lost fish populations due to acidification from the 1950s to the 1980s. In some parts of Europe, the anthropogenic SO2 emissions which lead to acid precipitation have been reduced by nearly 70 per cent from their maximum values (EEA 2001); there have also been reductions of some 40 per cent in the United States (US EPA 2000). This has resulted in a significant recovery of the natural acid balance, at least in Europe. On the contrary, as a result of the growing use of coal and other high sulphur fuels, increasing SO2 emissions in the Asia and Pacific Region are a serious environmental threat (UNEP 1999).

Air pollutant emissions have declined or stabilized in most industrialized countries, largely as a result of abatement policies developed and implemented since the 1970s. Initially governments tried to apply direct control instruments but these were not always costeffective. In the 1980s, policies were directed more towards cost-effective pollution abatement mechanisms that relied on a compromise between the cost of environmental protection measures and economic growth. The Polluter Pays Principle has become a basic concept in environmental policy planning.

Recent policy developments, at both national and regional levels, are based on economic and regulatory instruments, and technology improvement and transfer to enhance emission reductions. In the international arena, one of the most important political developments has been the Convention on Long- Range Transboundary Air Pollution (CLRTAP), adopted in 1979. Through a series of protocols establishing reduction objectives for the main air pollutants, this treaty has catalysed European, Canadian and US governments to implement national emission abatement policies (ECE 1995). The most recent protocol is the 1999 Protocol to Abate Acidification, Eutrophication and Ground-Level Ozone that sets up new reduction commitments for SO2, NOx, VOCs and ammonia (NH3) (ECE 2000).

Impacts associated with air pollution

Harmful substances emitted to the air affect both human health and ecosystems. Indoor and outdoor air pollution are estimated to be responsible for nearly 5 per cent of the global burden of disease. Air pollution aggravates and, possibly, even causes asthma and other allergic respiratory diseases. Adverse pregnancy outcomes, such as stillbirth and low birth weight, have also been associated with air pollution (Holdren and Smith 2000). It has been estimated that in developing countries about 1.9 million people die annually due to exposure to high concentrations of SPM in the indoor air environment of rural areas, while the excess mortality due to outdoor levels of SPM and SO2 amounts to about 500 000 people annually. Evidence is also emerging that particles with median aerodynamic diameter less than 2.5 Ám (PM2.5) affect human health significantly (WHO 1999).

Acid deposition is one of the causes of acidification of soil and water that results in declining fish stocks, decreasing diversity in acid-sensitive lakes and degradation of forest and soil. Excessive nitrogen (as nitrate and/or ammonium) promotes eutrophication, particularly in coastal areas. Acid rain damages ecosystems, provokes defoliation, corrosion of monuments and historic buildings and reduces agricultural yields.

World energy supply by fuel (million tonnes oil equivalent/year)

World energy supply is still dominated by the fossil fuels - coal, oil and gas

Source: IEA 2000

Stricter environmental regulation in the industrialized countries has triggered the introduction of cleaner technology and technological improvements, especially in the power generation and transport sectors. In the latter, a significant reduction in harmful emissions has been achieved due to the improved engine combustion cycle, increased fuel efficiency and the widespread introduction of catalytic converters (Holdren and Smith 2000). Lead emissions from gasoline additives have now declined to zero in many industrial countries (EEA 1999, US EPA 2000). In developing countries, however, the sources of emissions are more varied and include highly polluting power plants, heavy industry, vehicles and the domestic combustion of coal, charcoal and biomass. While the emission of pollutants can be significantly reduced for a small cost, few developing nations have made even small investments in pollution reduction measures, even though the environmental and population health benefits of such measures are evident (Holdren and Smith 2000, World Bank 1997).

Though measurable progress in industrial emission abatement has been achieved at least by the developed countries, transport has become one of the major sources of air pollution (particularly NOx and many carbon compounds) in many countries. High concentrations of these compounds in urban air can, under certain climatic conditions, result in photochemical smog that severely affects human health. In many urban centres and their surrounding areas, high concentrations of tropospheric O3 are an additional problem. Anthropogenic tropospheric ozone may be produced by reactions between NOx and VOCs on warm sunny days, especially in urban and industrial areas and in regions prone to stagnant air masses. This can have far-reaching implications since molecules of O3 have been found to travel large distances (up to 800 km) from emission sources (CEC 1997). Tropospheric O3 concentrations over large areas of Europe and some areas of North America are so high that not only is human health threatened but vegetation is also affected. For example, in the United States ground-level ozone has been estimated to cost more than US$500 million a year as a result of reductions in agricultural and commercial forest yields (US EPA 2000).

Migration of persistent organic pollutants

Persistent organic pollutants spread via a variety of mechanisms at different latitudes

Source: Wania and Mackay 1996

Urban air pollution is one of the most important environmental problems. In most European and North American cities, the concentrations of SO2 and SPM have decreased substantially in recent years (Fenger 1999, US EPA 2000). However, in many developing countries, rapid urbanization has resulted in increasing air pollution in many cities (Fenger 1999), WHO air quality guidelines are often not met and, in megacities such as Beijing, Calcutta, Mexico City and Rio de Janeiro, high levels of SPM prevail (World Bank 2001).

A final issue of global concern is that of persistent organic pollutants (POPs). These substances are known to decay slowly and they can be transported over long distances through the atmosphere (see illustration). High concentrations of some POPs are found in polar areas (Schindler 1999, Masclet and others 2000, Espeland and others 1997) with potentially serious regional environmental impacts. These compounds can also accumulate in animal fats, representing a health risk. The Stockholm Convention on Persistent Organic Pollutants, adopted in May 2001, sets out control measures covering handling of pesticides, industrial chemicals and unintended byproducts. The control provisions call for eliminating the production and use of intentionally produced POPs, and eliminating unintentionally produced POPs where feasible (UNEP 2001).