ambient air standard
the highest concentration of a specific air pollutant at a particular outdoor location, in a specified unit of time, that is not considered hazardous to humans: The ambient air standard for gas X is 3 parts per million per hour.
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Origin of ambient air standard
First recorded in 1970–75
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019