The National Emission Standards for Hazardous Air Pollutants (NESHAP) are air pollution standards issued by the United States Environmental Protection Agency (EPA). The standards, authorized by the Clean Air Act, are for pollutants not covered by the National Ambient Air Quality Standards (NAAQS) that may cause an increase in fatalities or in serious, irreversible, or incapacitating illness.

Maximum Achievable Control Technology standards

The standards for a particular source category require the maximum degree of emission reduction that the EPA determines to be achievable, which is known as the Maximum Achievable Control Technology (MACT) standards. These standards are authorized by Section 112 of the 1970 Clean Air Act and the regulations are published in the Code of Federal Regulations (CFR).

Pollutants

EPA regulates the following hazardous air pollutants with the MACT standards. For all listings above which contain the word "compounds" and for glycol ethers, the following applies: Unless otherwise specified, these listings are defined as including any unique chemical substance that contains the named chemical (i.e., antimony, arsenic, etc.) as part of that chemical's infrastructure.

Pollution sources

Most air toxics originate from human-made sources, including mobile sources (e.g., cars, trucks, buses) and stationary sources (e.g., factories, oil refineries, power plants), as well as indoor sources (e.g., building materials and activities such as cleaning). There are two types of stationary sources that generate routine emissions of air toxics: EPA published its initial list of source categories in 1992. Subsequently the agency issued several revisions and updates to the list and the regulatory promulgation schedule. 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 for some area sources that are of particular concern. EPA is required to review all source category regulations every eight years.