National Emissions Standards for Hazardous Air Pollutants
The National Emission Standards for Hazardous Air Pollutants are air pollution standards issued by the United States Environmental Protection Agency. The standards, authorized by the Clean Air Act, are for pollutants not covered by the National Ambient Air Quality Standards 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 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.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 as part of that chemical's infrastructure.
- X'CN where X = H' or any other group where a formal dissociation may occur. For example, KCN or Ca2
- Includes mono- and di- ethers of ethylene glycol, diethylene glycol, and triethylene glycol where
- Includes mineral fiber emissions from facilities manufacturing or processing glass, rock, or slag fibers of average diameter 1 micrometer or less.
- Includes organic compounds with more than one benzene ring, and which have a boiling point greater than or equal to 100 °C.
- A type of atom which spontaneously undergoes radioactive decay.
Pollution sources
Most air toxics originate from human-made sources, including mobile sources and stationary sources, as well as indoor sources. There are two types of stationary sources that generate routine emissions of air toxics:- Major sources are defined as sources that emit 10 or more tons per year of any of the listed toxic air pollutants, or 25 or more tons per year of a mixture of air toxics. These sources may release air toxics from fugitive emissions, when materials are transferred from one location to another, or during discharge through emission stacks or vents.
- Area sources consist of smaller facilities that release lesser quantities of toxic pollutants into the air. Area sources are defined as sources that do not emit more than 10 tons per year of a single air toxic or more than 25 tons per year of a combination of air toxics. Although the emissions from individual area sources are often relatively small, collectively their emissions can be of concern, particularly where large numbers of sources are located in heavily populated areas.