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MassDEP Ambient Air Toxics Guidelines

Guideline values intended to protect the general population, including sensitive populations, from adverse health effects.

Part of the Department of Environmental Protection (MassDEP), the Office of Research and Standards (ORS) develops health- and science-based air guidelines - known as Ambient Air Limits (AALs) and Threshold Effect Exposure Limits (TELs) - to evaluate potential human health risks from exposures to chemicals in air.

How MassDEP Develops & Uses Air Guideline Values

To determine the AALs and TELs for individual chemicals, MassDEP first develops:

  • Non-Threshold Effects Exposure Limits (NTELs) based on known or suspected carcinogenic health effects. The NTEL is a concentration associated with a one in a million excess lifetime cancer risk over a lifetime of continuous exposure; and
  • Threshold Effects Exposure Limits (TELs) based on non-cancer health effects. The TEL is a concentration intended to protect the general population, including sensitive populations such as children, from adverse health effects over a lifetime of continuous exposure. TELs take into account the fact that people may be exposed to a chemical from other sources, including indoor air, food, soil and water.

MassDEP compares the NTEL and the TEL and designates the lower concentration as the AAL. Since, in general, NTELs are lower than TELs, most AALs are based on the NTEL, or risk of excess cancer. For chemicals that do not pose cancer risks, the AAL is based on the TEL, and in this case the published AAL and TEL values are the same.

MassDEP uses AALs and TELs primarily in its air pollution control permitting program. The agency also uses AALs and TELs to evaluate the potential for health effects from chemicals present in ambient and indoor air.

It should be noted that exposure above an AAL or TEL does not automatically mean an individual will develop cancer or experience non-cancer health effects. However, the risk or probability of developing adverse effects increases with intensity and frequency of exposure.

Additional Resources for How MassDEP Develops & Uses Air Guideline Values

Current AALs & TELs

MassDEP releases AALs and TELs to the public by adding or updating guidelines and supporting information on this web page. You may sign up to be notified when new values are published.

Table of MassDEP Air Guideline Values

Chemical Name &
CAS Number

Threshold Effects Exposure Limit (TEL)
(24-Hour Average)


ug/m3  |  ppb

Allowable Ambient Limit (AAL)
(Annual Average)

ug/m3  |  ppb

Last Updated

Acetaldehyde
75070

30  |  20

0.4  |  0.2

2015

Acrolein
107028

0.07  |  0.03

0.07  |  0.03

2014

Acetone
67641

160.54  |  68.03

160.54  |  68.03

1990

Acrylonitrile
107131

0.4  |  0.18

0.01  |  0.0046

1995

Alkanes/Alkenes
(not to exceed 25% n-hexane)

95.24  |  -

47.62  |  -

1990

Ammonia
7664417

100  |  100

100  |  100

2011

Aniline
62533

0.2  |  0.053

0.1  |  0.026

1995

Antimony
7440360

0.02  |  -

0.02  |  -

2015

Arsenic
7440382

0.003  |  -

0.0003  |  -

2011

Asbestos
1332214

0.0002
f/cm3  |  -

0.000004
f/cm|  -

1990

Benzene
71432

0.6  |  0.2

0.1  |  0.03

2015

Benzyl Chloride
100447

14.08  |  2.72

0.94  |  0.18

1990

Beryllium
7440417

0.001  |  -

0.0004  |  -

1990

1,3-Butadiene
106990

1.20  |  0.54

.003  |  0.002

1990

n-Butyl Alcohol
71363

412.24  |  136.05

412.24  |  136.05

1990

Cadmium
7440439

0.002  |  -

0.0002  |  -

2014

Calcium Chromate
13765190

0.003  |  -

0.0001  |  -

1990

Carbon Disulfide
75150

0.1  |  0.032

0.1  |  0.032

1995

Carbon Tetrachloride
56235

85.52  |  13.61

0.07  |  0.01

1990

Carbonyl Sulfide
463581

0.1  |  0.041

0.1  |  0.041

1995

Chlordane
57749

0.14  |  0.008

0.03  |  0.002

1990

Chlorine
7782505

3.95  |  1.36

3.95  |  1.36

1990

Chlorobenzene
108907

93.88  |  20.41

6.26  |  1.36

1990

Chloroethane
75003

717.55  |  272.11

358.78  |  136.05

1990

Chloroform
67663

132.76  |  27.21

0.04  |  0.01

1990

Chloroprene
126998

0.98  |  0.27

0.98  |  0.27

1990

Chromic Acid
7738945

0.003  |  -

0.0001  |  -

1990

Chromium (metal)
7440473

1.36  |  -

0.68  |  -

1990

Chromium (VI) Compounds

0.003  |  -

0.0001  |  -

1990

Copper
7440508

0.54  |  -

0.54  |  -

1990

p-Cresol
106445

24.05  |  5.44

12.02  |  2.72

1990

Cyclohexane
110827

280.82  |  81.63

280.82  |  81.63

1990

o-Dichlorobenzene
95501

81.74  |  13.61

81.74  |  13.61

1990

p-Dichlorobenzene
106467

122.61  |  20.41

0.18  |  0.03

1990

1,2-Dichloroethane
107062

11.01  |  2.72

0.04  |  0.01

1990

1,2-Dichloroethylene
540590

215.62  |  54.42

107.81  |  27.21

1990

Dichloromethane (Methylene Chloride)
75092

100  |  30

60  |  20

2014

1,2-Dichloropropane
78875

0.9  |  0.19

0.05  |  0.01

1995

Diethylamine
109897

8.13  |  2.72

4.07  |  1.36

1990

Di(2-ethylhexyl)phthalate
117817

1.36  |  0.09

0.77  |  0.05

1990

Dimethylformamide
68122

6  |  2.01

3  |  1.004

1995

1,4-Dioxane
123911

24.49  |  6.80

0.24  |  0.07

1990

Diphenyl
92524

0.34  |  0.05

0.09  |  0.01

1990

Diphenylamine
122394

2.72  |  0.39

0.68  |  0.10

1990

Epichlorohydrin
106898

0.08  |  0.021

0.08  |  0.021

1995

Ethanol
64175

51.24  |  27.21

51.24  |  27.21

1990

Ethyl Acetate
141786

391.84  |  108.84

391.84  |  108.84

1990

Ethyl Acrylate
140885

0.56  |  0.14

0.28  |  0.07

1990

Ethylbenzene
100414

300  |  69.09

300  |  69.09

1995

Ethylene Glycol
107211

34.50  |  13.61

34.50  |  13.61

1990

Ethyl Ether
60297

329.80  |  108.84

164.90  |  54.42

1990

Fluoride
16984488

6.80  |  8.76

6.80  |  8.76

1990

Formaldehyde
50000

2  |  2

0.08  |  0.06

2011

Furan
110009

0.40  |  0.14

0.02  |  0.007

1990

Heptachlor
76448

0.14  |  0.009

0.001  |  0.0001

1990

Hexachlorocyclopentadiene
77474

0.006  |  0.0005

0.006  |  0.0005

1990

Hexachloroethane
67721

0.53  |  0.05

0.25  |  0.03

1990

2-Hexanone
591786

10.88  |  2.66

10.88  |  2.66

1990

Hydrazine
302012

0.04  |  0.03

0.0002  |  0.0002

2011

Hydrogen Bromide
10035106

5  |  1.51

5  |  1.51

1995

Hydrogen Chloride
7647010

7  |  4.69

7  |  4.69

1995

Hydrogen Cyanide
74908

0.6  |  0.54

0.3  |  0.27

1995

Hydrogen Fluoride
7664393

0.68  |  0.83

0.34  |  0.42

1990

Hydrogen Sulfide
7783064

0.9  |  0.65

0.9  |  0.65

1995

Isoamyl Acetate
123922

144.76  |  27.21

144.76  |  27.21

1990

Isobutyl Acetate
110190

193.77  |  40.82

193.77  |  40.82

1990

Isobutyl Alcohol
78831

41.22  |  13.61

41.22  |  13.61

1990

Isopropyl Acetate
108214

283.81  |  68.03

283.81  |  68.03

1990

Lead
7439921

0.14  |  -

0.07  |  -

1990

Lead Subacetate
1335326

0.14  |  -

0.01  |  -

1990

Lindane
58899

0.14  |  0.11

0.003  |  0.0002

1990

Maleic Anhydride
108316

0.1  |  0.02

0.1  |  0.02

2011

Mercury (elemental)
7439976

0.14  |  -

0.07  |  -

1990

Mercury (inorganic)

0.14  |  -

0.01  |  -

1990

Mercury (methyl-)
22967926

0.003  |  -

0.0014  |  -

1990

Methanol
67561

7.13  |  5.44

7.13  |  5.44

1990

2-Methoxy Ethanol
109864

3  |  0.96

2  |  0.64

1995

Methyl Acrylate
96333

9.57  |  2.72

4.79  |  1.36

1990

Methyl Bromide
74839

5.28  |  1.36

2.64  |  0.68

1990

Methyl Ethyl Ketone (MEK)
78933

200  |  67.82

10  |  3.39

1995

Methyl Isobutyl Ketone (MIBK)
108101

55.70  |  13.61

55.70  |  13.61

1990

Methyl Methacrylate
80626

22.27  |  5.44

22.27  |  5.44

1990

Naphthalene (including 2-methylnaphthalene)
91203

14.25  |  2.72

14.25  |  2.72

1990

Nickel (metal)
7440020

0.27  |  -

0.18  |  -

1990

Nickel Oxide
1313991

0.27  |  -

0.01  |  -

1990

Nitrobenzene
98953

13.69  |  2.72

6.84  |  1.36

1990

Pentachlorophenol
87865

0.01  |  0.001

0.01  |  0.001

1990

Phenol
108952

52.33  |  13.61

52.33  |  13.61

1990

Phosphoric Acid
7664382

0.27  |  0.07

0.27  |  0.07

1990

Phthalic Anhydride
85449

1.65  |  0.27

0.82  |  0.14

1990

PCBs
1336363

0.003  |  -

0.0005  |  -

1990

Propyl Alcohol
71238

133.63

54.42

133.63

54.42

1990

Propylene Oxide
75569

6

2.53

0.3

0.13

1995

Resorcinol
108463

12.24  |  2.72

3.06  |  0.68

1990

Selenium
7782492

0.54  |  -

0.54  |  -

1990

Selenium Sulfide
7446346

0.54  |  -

0.05  |  -

1990

Styrene
100425

200  |  46.96

2  |  0.47

1995

Sulfuric Acid
7664939

2.72  |  0.68

2.72  |  0.68

1990

1,1,2,2-Tetrachloro-
1,2-Difluoroethane
76120

1133.33  |  136.05

566.67  |  68.03

1990

1,1,2,2-Tetrachloroethane
79345

18.67  |  2.72

0.02  |  0.003

1990

Tetrachloroethylene
127184

8  |  1

0.3  |  0.04

2015

Tetrahydrofuran
109999

160.35  |  54.42

80.18  |  27.21

1990

Toluene
108883

80  |  21.23

20  |  5.31

1995

Toluene Diisocyanate
584849

0.10  |  0.01

0.10  |  0.01

1990

o-Toluidine
95534

2.38  |  0.54

0.17  |  0.04

1990

1,1,1-Trichloroethane
71556

1038.37  |  190.48

1038.37  |  190.48

1990

1,1,2-Trichloroethane
79005

14.84  |  2.72

0.06  |  0.01

1990

Trichloroethylene
79016

36.52  |  6.80

0.61  |  0.11

1990

2,4,6-Trichlorophenol
88062

-  |  -

0.16  |  -

1990

Triethylamine
121448

1  |  0.24

0.7  |  0.17

1995

Vanadium
1314621

0.27  |  -

0.27  |  -

1990

Vanadium Pentoxide
1314621

0.14  |  0.02

0.03  |  0.005

1990

Vinyl Acetate
108054

30  |  8.52

8  |  2.27

1995

Vinyl Chloride
75014

3.47  |  1.36

0.38  |  0.15

1990

Vinylidene Chloride
75354

1.08  |  0.27

0.02  |  0.01

1990

Xylenes (m-,o-,p- isomers)
1330207

11.80  |  2.72

11.80  |  2.72

1990

Note: All new and revised values are expressed in ug/m3 to one significant figure. Values are also presented in units of ppb for the convenience of users. From 2011 forward, values in units of ppb are calculated from the value in units of ug/m3 after it has been rounded to one significant figure. Concentrations measured in units of ppb can be transformed to ug/m3 using all significant figures applicable to the measured concentration in ppb, assuming the molecular conversion factor has an infinite number of significant figures, and then rounded to one significant figure for comparison to the Air Guidelines. Values derived in 1995 are presented in ppb without rounding.

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