Background Concentration Estimates

Note: EPA no longer updates this information, but it may be useful as a reference or resource.

National-Scale Air Toxics Assessment
Background Concentration Estimates

Pollutant	Background Concentration (µg/m3)
Benzene	0.48
Carbon tetrachloride	0.88
Chloroform	0.083
Ethylene dibromide	0.0077
Ethylene dichloride	0.061
Formaldehyde	0.25
Hexachlorobenzene	.000093
Mercury compounds	0.0015
Methylene chloride	0.15
Polychlorinated biphenyls	0.00038
Perchloroethylene (Tetrachloroethylene)	0.14
Trichloroethylene	0.081