Air quality criteria

From Glossary of Meteorology

air quality criteria

Quantitative and qualitative indications of the relationships between exposure to pollutants and effects on human health, animals, plants, and materials.

These are descriptive effects of pollution as a function of concentration averaged over various time durations. A time-averaged concentration is used because exposure to a high concentration of pollutants during a short time might have an impact equivalent to an exposure to a lower concentration over a longer time.
Compare air quality standards.