Pollutant Standard Index

A number used to indicate the air quality at a given time and location relative to the National Ambient Air QualityStandards set up by the Environmental Protection Agency to measure the health impacts of air pollution. EPA established standard measures for six pollutants: carbon monoxide, ozone, particulate matter, lead, sulfur dioxide and nitrous oxide. The transportation provisions of the Clean Air Act focus on ozone and carbon monoxide standards. More Standards. A PSI of 100 for a given air pollutant represents a concentration equal to the respective air quality standard.