The maximum concentration of a pollutant which is considered harmless to healthy adults
during their working hours, assuming they breathe uncontaminated air at all other
times.
Source:
PAC, 1990, 62, 2167
(Glossary of atmospheric chemistry terms (Recommendations 1990))
on page 2200
See also:
PAC, 1993, 65, 2003
(Glossary for chemists of terms used in toxicology (IUPAC Recommendations 1993))
on page 2066