ceiling value (CV) in photochemistry, in atmospheric chemistry

https://dx.doi.org/10.1351/goldbook.CT06815
Airborne concentration of a potentially toxic substance which should never be exceeded in a worker’s breathing zone.
Source:
PAC, 2004, 76, 1033 (Glossary of terms used in toxicokinetics (IUPAC Recommendations 2003)) on page 1043