Revised September 2000
including WHO's 1999 Guidelines for Air Pollution Control
Exposure to air pollution is as old as the use of fire by human beings
Air pollution, both indoors and outdoors, is a major environmental health problem affecting developed and developing counties alike. It comes from sources of dust, gases and smoke, and is generated mainly by human activities but also naturally. When inhaled, air pollutants affect the lung and respiratory tract but can also be taken up and transported by the blood stream throughout the body. Through deposition in the environment, air pollutants can also contaminate food and water.
Every year millions of people die or suffer serious health effects from air pollution: mainly respiratory diseases, asthma, chronic obstructive pulmonary disease, cardiovascular disease and cancer of the lung.
The effects of air pollution depend on levels of exposure and susceptibility of the exposed population. People suffering from respiratory conditions such as asthma, both the very young and old, and people living in poverty, are particularly at risk.
Air pollution also affects the workforce, and indoor air pollution is the primary cause in as many as 50 million cases of occupational chronic respiratory disease each year a third of all occupational illnesses. These are widespread, debilitating and affect people in their social and economic prime of life. They are preventable with a minimum of resources.
Air pollution and pollutants
The common picture of air pollution is of smoking industrial chimneys and traffic exhausts affecting the surrounding populations ambient air pollution. Even though the main sources of air pollutants are man-made traffic and industry natural sources also contribute (e.g. volcanoes).
Indoor air pollutants are an even greater threat to the health of millions. In developing countries, the domestic use of coal and biomass materials as fuel for heating and cooking is a major source of indoor pollution. The greatest threat in this case is to women and children living in poverty.
Air pollutants are classified as suspended particulate matter, gases and vapours that are present in the atmosphere in abnormally high concentrations.
Concentrations of sulphur dioxide and suspended particulate matter are decreasing in developed countries, while those of NOX and ozone are either constant or increasing. In developing countries, increasing traffic and its exhaust as well as industrial emissions are raising concentrations of SO2, NOX and O3 and suspended particulate matter.
Ambient air pollution
Without proper controls, industry is a major source of air pollution. In this way, industrial operations can affect the health of workforces, the general environment and the health of nearby (and sometimes very far removed) populations.
Indoor air pollution
Even today, homes of the poor in developing counties are dangerous, unhealthy places a rule of thumb states that a pollutant released indoors is 1000 times more likely to reach people's lungs than a pollutant released outdoors.
Some 2000 million people throughout the world use wood or other biomass fuels (cow dung, crop residues and grass) for cooking and heating. The domestic burning of these fuels is an inefficient process that produces many pollutants, some of which may be carcinogenic. The problems are worsened in areas where people spend most of their time indoors.
Coal burning for heating and cooking in developing countries results in indoor particle concentrations of up to 10,000 µg/m³, a level that is much higher even than ambient concentrations in polluted cities in Asia.
Air pollution has long been associated with industrial processes and energy generation. Pollution control followed the European Industrial Revolution and increased in importance after World War II with economic expansion. Various steps have been taken to prevent the destruction of the environment and the removal or at least minimizing hazards to human health.
Guidelines and standards
WHO has produced the WHO Air Quality Guidelines. They are available from WHO or on the web site at: www.who.int/peh/air/airindex. The Guidelines provide background information which enables countries to set their national or regional air quality standards in the context of existing environmental, social, economic and cultural conditions.
The Guidelines set out the range of ambient concentrations in exposure-response relationships and give guideline values; the air quality guideline value defines a concentration of air pollutant below which no adverse effect to human health is expected. Guideline values for 38 non-carcinogenic compounds and some carcinogens are set in relation to different exposure times. The table below gives some examples of the guideline value for common gaseous pollutants.
WHO Guidelines values (1999) for common pollutants
Application of the WHO Air Quality Guidelines should help significantly to reduce the burden of excess mortality and preventable disability from a highly preventable source of ill-health.
Air quality management
For more than 20 years the WHO with the UN Environmental Programme (UNEP) assessed trends in ambient air pollution until this programme was replaced by the Air Management Information System (AMIS). Under the umbrella of WHO's Healthy Cities Programme, AMIS provides a means of actively sharing information between its members through a set of user-friendly databases. It is planned as a component of WHO's Global Air Quality Partnership, which brings together:
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Further information can be obtained from the web site of the responsible WHO programme at: http://www.who.int/peh/.