Toxic pollutant sources fall into three major categories:

Major Point Source

A major source is one that emits over 10 tons of any single toxic pollutant, or over 25 tons of any combination of toxic pollutants per year. Examples of a major point source would be power plants, chemical plants, refineries, and large municipal waste combustors. EPA has estimated that 24 percent of all man-made air toxic emissions come from major sources (from NATA).

Area Source

An area source is a concentrated number of smaller toxic sources, each emitting less than 10 tons per year of any single toxic and less than 25 tons per year of combined toxics, that when considered collectively is a major contributor to toxics in the environment. Examples of area sources include gas stations, dry cleaners, print shops, autobody shops, furniture manufacturers, and home sources such as wood stoves, pesticides, and cleaners. Area sources contribute to 26 percent of all man-made air toxic emissions according to EPA estimates.

Mobile Source

As the name implies, mobile sources include cars, trucks, buses, boats, trains, lawnmowers​, tractors, and recreational vehicles. The EPA estimates that 50 percent of all man-made air toxic emissions come from mobile sources. Mobile sources produce air toxics through tailpipe emissions as well as evaporation from the engine, the fuel system, and when refueling.