Air Quality Index (AQI) (Environmental Glossary)

Air Quality Index (AQI): An index for reporting daily air quality. It determines how clean or polluted air is and what associated health effects might be of concern. The AQI focuses on health effects you may experience within a few hours or days after breathing polluted air. EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. For each pollutant, EPA has established national air quality standards to protect public health. Ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health in this country.