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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.[1]

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.[2] 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).[3]


EPA regulates the following hazardous air pollutants with the MACT standards.

CAS Number Chemical Name Notes
75-07-0 Acetaldehyde
60-35-5 Acetamide
75-05-8 Acetonitrile
98-86-2 Acetophenone (Methyl Phenyl Ketone)
53-96-3 2-Acetylaminofluorene
107-02-8 Acrolein
79-06-1 Acrylamide
79-10-7 Acrylic acid
107-13-1 Acrylonitrile
107-05-1 Allyl chloride (3-Chloropropene)
92-67-1 4-Aminobiphenyl
62-53-3 Aniline
90-04-0 o-Anisidine
1332-21-4 Asbestos
71-43-2 Benzene including benzene from gasoline
92-87-5 Benzidine
98-07-7 Benzotrichloride
100-44-7 Benzyl chloride
92-52-4 Biphenyl
117-81-7 Bis(2-ethylhexyl)phthalate (DEHP)
542-88-1 Bis(chloromethyl)ether
75-25-2 Bromoform (Tribromomethane)
106-99-0 1,3-Butadiene
156-62-7 Calcium cyanamide
105-60-2 Caprolactam Delisted on June 18, 1996
133-06-2 Captan
63-25-2 Carbaryl
75-15-0 Carbon disulfide
56-23-5 Carbon tetrachloride (Tetrachloromethane)
463-58-1 Carbonyl sulfide
120-80-9 Catechol
133-90-4 Chloramben
57-74-9 Chlordane
7782-50-5 Chlorine
79-11-8 Chloroacetic acid
532-27-4 2-Chloroacetophenone
108-90-7 Chlorobenzene
510-15-6 Chlorobenzilate
67-66-3 Chloroform (Trichloromethane)
107-30-2 Chloromethyl methyl ether
126-99-8 Chloroprene
1319-77-3 Cresols/Cresylic acid (isomers and mixture)
95-48-7 o-Cresol
108-39-4 m-Cresol
106-44-5 p-Cresol
98-82-8 Cumene
94-75-7 2,4-D, salts and esters
3547-04-4 Dichlorodiphenyldichloroethylene (DDE)
334-88-3 Diazomethane
132-64-9 Dibenzofurans
96-12-8 1,2-Dibromo-3-chloropropane (DBCP)
84-74-2 Dibutylphthalate
106-46-7 1,4-Dichlorobenzene (p-Dichlorobenzene)
91-94-1 3,3'-Dichlorobenzidine
111-44-4 Dichloroethyl ether (Bis(2-chloroethyl)ether)
542-75-6 1,3-Dichloropropene
62-73-7 Dichlorvos
111-42-2 Diethanolamine
64-67-5 Diethyl sulfate
119-90-4 3,3'-Dimethoxybenzidine
60-11-7 Dimethyl aminoazobenzene
119-93-7 3,3'-Dimethyl benzidine
79-44-7 Dimethylcarbamoyl chloride
68-12-2 Dimethyl formamide
57-14-7 1,1-Dimethyl hydrazine
131-11-3 Dimethyl phthalate
77-78-1 Dimethyl sulfate
121-69-7 N,N-Dimethylaniline Clean Air Act erroneously lists N,N-Diethylaniline
534-52-1 4,6-Dinitro-o-cresol, and salts
51-28-5 2,4-Dinitrophenol
121-14-2 2,4-Dinitrotoluene
123-91-1 1,4-Dioxane (1,4-Diethyleneoxide)
122-66-7 1,2-Diphenylhydrazine
106-89-8 Epichlorohydrin (l-Chloro-2,3-epoxypropane)
106-88-7 1,2-Epoxybutane
140-88-5 Ethyl acrylate
100-41-4 Ethyl benzene
51-79-6 Ethyl carbamate (Urethane)
75-00-3 Ethyl chloride (Chloroethane)
106-93-4 Ethylene dibromide (1,2-Dibromoethane)
107-06-2 Ethylene dichloride (1,2-Dichloroethane)
107-21-1 Ethylene glycol
151-56-4 Ethylene imine (Aziridine)
75-21-8 Ethylene oxide
96-45-7 Ethylene thiourea
75-34-3 Ethylidene dichloride (1,1-Dichloroethane)
50-00-0 Formaldehyde
76-44-8 Heptachlor
118-74-1 Hexachlorobenzene
87-68-3 Hexachlorobutadiene
77-47-4 Hexachlorocyclopentadiene
67-72-1 Hexachloroethane
822-06-0 Hexamethylene-1,6-diisocyanate
680-31-9 Hexamethylphosphoramide
110-54-3 Hexane
302-01-2 Hydrazine
7647-01-0 Hydrochloric acid
7664-39-3 Hydrogen fluoride (Hydrofluoric acid)
7783-06-4 Hydrogen sulfide Delisted on December 4, 1991
123-31-9 Hydroquinone
78-59-1 Isophorone
58-89-9 Lindane (all isomers)
108-31-6 Maleic anhydride
67-56-1 Methanol
72-43-5 Methoxychlor
74-83-9 Methyl bromide (Bromomethane)
74-87-3 Methyl chloride (Chloromethane)
71-55-6 Methyl chloroform (1,1,1-Trichloroethane)
78-93-3 Methyl ethyl ketone (2-Butanone or MEK) Delisted on December 19, 2005
60-34-4 Methyl hydrazine
74-88-4 Methyl iodide (Iodomethane)
108-10-1 Methyl isobutyl ketone (Hexone or MIBK) currently under review for delisting
624-83-9 Methyl isocyanate
80-62-6 Methyl methacrylate
1634-04-4 Methyl tert-butyl ether
101-14-4 4,4'-Methylene bis(2-chloroaniline)
75-09-2 Methylene chloride (Dichloromethane)
101-68-8 Methylene diphenyl diisocyanate (MDI) currently under review for delisting
101-77-9 4,4'-Methylenedianiline
91-20-3 Naphthalene
98-95-3 Nitrobenzene
92-93-3 4-Nitrobiphenyl
100-02-7 4-Nitrophenol
79-46-9 2-Nitropropane
684-93-5 N-Nitroso-N-methylurea
62-75-9 N-Nitrosodimethylamine
59-89-2 N-Nitrosomorpholine
56-38-2 Parathion
82-68-8 Pentachloronitrobenzene (Quintobenzene)
87-86-5 Pentachlorophenol
108-95-2 Phenol
106-50-3 p-Phenylenediamine
75-44-5 Phosgene
7803-51-2 Phosphine
7723-14-0 Phosphorus
85-44-9 Phthalic anhydride
1336-36-3 Polychlorinated biphenyls (Aroclors)
1120-71-4 1,3-Propane sultone
57-57-8 beta-Propiolactone
123-38-6 Propionaldehyde
114-26-1 Propoxur (Baygon)
78-87-5 Propylene dichloride (1,2-Dichloropropane)
75-56-9 Propylene oxide
75-55-8 1,2-Propylenimine (2-Methyl aziridine)
91-22-5 Quinoline
106-51-4 Quinone
100-42-5 Styrene
96-09-3 Styrene oxide
1746-01-6 2,3,7,8-Tetrachlorodibenzo-p-dioxin
79-34-5 1,1,2,2-Tetrachloroethane
127-18-4 Tetrachloroethylene (Perchloroethylene)
7550-45-0 Titanium tetrachloride
108-88-3 Toluene
95-80-7 2,4-Toluene diamine
584-84-9 2,4-Toluene diisocyanate
95-53-4 o-Toluidine
8001-35-2 Toxaphene (chlorinated camphene)
120-82-1 1,2,4-Trichlorobenzene
79-00-5 1,1,2-Trichloroethane
79-01-6 Trichloroethylene
95-95-4 2,4,5-Trichlorophenol
88-06-2 2,4,6-Trichlorophenol
121-44-8 Triethylamine
1582-09-8 Trifluralin
540-84-1 2,2,4-Trimethylpentane
108-05-4 Vinyl acetate
593-60-2 Vinyl bromide (Bromoethene)
75-01-4 Vinyl chloride (Chloroethene)
75-35-4 Vinylidene chloride (1,1-Dichloroethylene)
1330-20-7 Xylenes (isomers and mixture)
95-47-6 o-Xylenes
108-38-3 m-Xylenes
106-42-3 p-Xylenes
n/a Antimony Compounds
n/a Arsenic Compounds inorganic including arsine
n/a Beryllium Compounds
n/a Cadmium Compounds
n/a Chromium Compounds
n/a Cobalt Compounds
n/a Coke Oven Emissions
n/a Cyanide Compounds1
n/a Glycol ethers2
n/a Lead Compounds
n/a Manganese Compounds
n/a Mercury Compounds
n/a Fine mineral fibers3
n/a Nickel Compounds
n/a Polycylic Organic Matter4
n/a Radionuclides5 including radon
n/a Selenium Compounds

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.

n = 1, 2, or 3
R = alkyl C7 (chain of 7 carbon atoms) or less; or phenyl or alkyl substituted phenyl
R' = H or alkyl C7 or less; or OR' consisting of carboxylic acid ester, sulfate, phosphate, nitrate, or sulfonate. Polymers are excluded from the glycol category, as well as surfactant alcohol ethoxylates (where R is an alkyl C8 or greater) and their derivatives, and ethylene glycol monobutyl ether (CAS 111-76-2).

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:

  1. 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 (equipment leaks), when materials are transferred from one location to another, or during discharge through emission stacks or vents.
  2. 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.

EPA published its initial list of source categories in 1992.[5] 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.[6]

See also


  1. ^ United States. Clean Air Amendments of 1970. Pub. L.Tooltip Public Law (United States) 91–604 Section 112. 42 U.S.C. § 7412
  2. ^ "Reducing Emissions of Hazardous Air Pollutants". Washington, D.C.: United States Environmental Protection Agency (EPA). 2021-01-26.
  3. ^ EPA. "National Emission Standards for Hazardous Air Pollutants." Code of Federal Regulations, 40 CFR 61. “National Emission Standards for Hazardous Air Pollutants for Source Categories.” 40 CFR 63
  4. ^ "Initial List of Hazardous Air Pollutants with Modifications". EPA. 2022-01-05.
  5. ^ EPA (1992-07-16). "Initial List of Categories of Sources Under Section 112(c)(1) of the Clean Air Act Amendments of 1990." Federal Register, 57 FR 31576.
  6. ^ "Risk and Technology Review of the National Emissions Standards for Hazardous Air Pollutants". Stationary Sources of Air Pollution. EPA. 2022-02-08.