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Area sources are sources of pollution that consist of many smaller emitters that are distributed across a geographic area^[1]. Examples of area sources include gas stations, dry-cleaners, print shops, autobody shops, furniture manufactures, and home sources such as wood stoves, pesticides, and cleaners. As defined by the EPA, to qualify as an area source, the source must emit less than 10 tons of a hazardous air pollutant, or HAP, anually. If the source is emitting numerous HAPs, then the emissions should not exceed 25 tons cumulatively^[2]. Area sources contribute to 26 percent of all man-made air toxic emissions according to EPA estimates. Area sources differ from major point sources, for point sources emit over 10 tons of one or over 25 of numerous hazardous air pollutants. These major point sources are one single identifiable emitter, such as power plants and refineries^[3]. Although individual area sources emit small quantities of pollutants, they are spread out across regions and are found in large numbers. This results in a substantial contribution to air pollution.

For example, area sources of air pollution are air pollutant emission sources which operate within a certain locale. The U.S. Environmental Protection Agency has categorized 70 different categories of air pollution area source.^[4] Locomotives operating on certain linear tracks are examples of a line source, whereas locomotives operating within a railyard are an example of an area source of pollution. Other area sources of air pollution are:

• Multiple flue gas stacks within a single industrial plant
• Open burning and forest fires
• Evaporation losses from large spills of volatile liquids

Exposure to HAPs from area sources of pollution have been associated with many minor and some serious adverse health effects. Some serious health effects that HAPs may cause are cancer, birth defects, and blood disorders. HAPs may also cause immune system, reproductive system, and respiratory system damage. Minor health effects include skin and eye irritation, nausea, headaches, fatigue, and changes in behavior^[5]. Exposure to most HAPs comes from breathing in air containing them, as well as the ingestion of waters where HAPs have been deposited^[6].

Water pollution manifestations of an area source—often called nonpoint source pollution—include:

• Surface runoff of fertilizer or pesticides from rainfall or irrigation water
• Widespread failure of a septic drain field
• Dispersal of an oil spill in a water body.^[7]

In the 1950s or earlier hydrology transport models appeared to calculate surface runoff, primarily for flood forecasting. Beginning in the early 1970s computer models were developed to analyze the transport of runoff carrying water pollutants, which considered dissolution rates of various chemicals, infiltration into soils and ultimate pollutant load delivered to receiving waters. One of the earliest models addressing chemical dissolution in runoff and resulting transport was developed in the early 1970s by the United States Environmental Protection Agency.^{[8][full citation needed]} This computer model formed the basis of much of the regulatory framework that led to strategies for water pollution control via land use and chemical handling techniques. People produce so much trash that half of it goes in water sources.^{[citation needed]}

• Air pollution dispersion terminology
• Atmospheric dispersion modeling
• List of atmospheric dispersion models
• Line source
• Point source (pollution)
• Roadway air dispersion modeling
• Volume source (pollution)

• C. Michael Hogan, Leda Patmore, Gary Latshaw, Harry Seidman et al. 1973. Computer modeling of pesticide transport in soil for five instrumented watersheds, U.S. Environmental Protection Agency Southeast Water laboratory, Athens, Ga. by ESL Inc., Sunnyvale, California
• Arnold W. Reitze, J. B. Shapiro and Maurice C. Shapiro. 2005. Stationary Source Air Pollution Law, Published by Environmental Law Institute, 500 pages ISBN 1-58576-091-9, ISBN 978-1-58576-091-6