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In many industrialized cities across the globe, pollution from stationary industrial sources is a major component of urban air quality management. U.S. EPA has categorized sources of hazardous air pollutants (HAPs), which are listed by industry group. As defined by the U.S. Clean Air Act, there are two types of stationary sources that generate routine emissions of air toxics: major or area. For each listed source category, EPA indicates whether the sources are considered to be "major" sources or "area" sources. The 1990 Clean Air Act Amendments direct EPA to set standards for all major sources of air toxics (and some area sources that are of particular concern).


Mobile sources (e.g., cars, trucks, trains, airplanes) pollute the air through combustion and fuel evaporation. These emissions contribute greatly to air pollution and are the primary cause of air pollution in many urban areas. U.S. EPA's Office of Transportation and Air Quality Utilities web site provides basic information on mobile sources, including definitions of on-road vehicles and non-road vehicles, engines, and equipment, and has links to information on the main pollutants from mobile sources (carbon monoxide, hydrocarbons, nitrogen oxides, and particulate matter), and solutions and results in the U.S.

In addition, the Clear Air Initiative web page provides extensive mobile source information and publications on the global scale, as well as regionally for Asia, Europe, Latin America, and Sub-Saharan Africa.


Air pollution from agricultural sources is derived from emissions of nitrogen and gaseous sulfur compounds from animal and crop agriculture as well as activities such as prescribed burning. In the U.S., the degree to which ambient air emissions from farming practices are allowed are location-specific (specific to a geographic area) within each State Implementation Plan. Visibility standards may also apply through the State Implementation Plan.

Indoor Air

While pollutant levels from individual sources may not pose a significant health risk by themselves, most homes have more than one source that contributes to indoor air pollution. There can be a serious risk from the cumulative effects of these sources. Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes. There are many sources of indoor air pollution in any home. These include combustion sources such as oil, gas, kerosene, coal, wood, and tobacco products; building materials and furnishings as diverse as deteriorated, asbestos-containing insulation, wet or damp carpet, and cabinetry or furniture made of certain pressed wood products; products for household cleaning and maintenance, personal care, or hobbies; central heating and cooling systems and humidification devices; and outdoor sources such as radon, pesticides, and outdoor air pollution.

See U.S. EPA's Indoor Air Quality site, U.S. EPA's Basic Information About Indoor Air Quality, and the World Bank Indoor Air Quality site for more information on issues related to indoor air in the home.

Indoor air quality problems are not limited to homes. In fact, many office buildings have significant air pollution sources. See U.S. EPA's site on Indoor Air Quality in Large Buildings for more information about commercial issues related to indoor air.


This includes sources of pollutants from other sources not covered in the above category (e.g., light industry). No further information is available for this category at this time.


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