Ground-level ozone, however, is the main contributor to urban smog. Ground-level ozone is the product of reactions among chemicals produced by burning coal, gasoline and other fuels, and chemicals in products such as solvents and paints. A criteria air pollutant. Coarse particulates include dust, soot, and other small particles that are released into the air, usually by activities that involve the crushing, grinding, and abrading of surfaces. Construction activities, the burning of wood, agricultural burning, and certain industrial processes also create coarse particulate matter.
Fine particulates result primarily from combustion processes.
The burning of different fuels, whether from industrial, residential, or mobile sources, releases very small particles that can coalesce in the air and react with other chemicals. A document resembling a license that is required by the Clean Air Act for major sources of air pollution, such as power plants and chemical factories, and in some cases, smaller polluters. Permits are typically granted by state environmental agencies, but if the EPA has disapproved all or part of a state permit program, the EPA will issue the permits in that state. The 1990 Clean Air Act Amendments set out requirements for permit applications, including provisions for members of the public to participate in state and EPA reviews of permit applications. Permits are intended to provide a central location for information on all regulated pollutants emitted by a source, including which pollutants are being released, how much the emission source is allowed to release, and the program that will be used to meet pollutant release requirements.