FAQ Air Quality Index
What is the U.S. Air Quality Index (AQI)?
The U.S. AQI is EPA’s index for reporting air quality.
How does the AQI work?
Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality.
A Guide to Air Quality and Your Health
This booklet explains EPA’s Air Quality Index (AQI) and the health effects of major air pollutants.
For each pollutant, an AQI value of 100 generally corresponds to an ambient air concentration that equals the level of the short-term national ambient air quality standard for the protection of public health.
AQI values at or below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is unhealthy: at first for certain sensitive groups of people, then for everyone as AQI values get higher.
The AQI is divided into six categories. Each category corresponds to a different level of health concern. Each category also has a specific color. The color makes it easy for people to quickly determine whether air quality is reaching unhealthy levels in their communities.
Five major pollutants
EPA establishes an AQI for five major air pollutants regulated by the Clean Air Act. Each of these pollutants has a national air quality standard set by EPA to protect public health:
- Ground-level ozone
- Particle pollution (also known as particulate matter, including PM2.5 and PM10)
- Carbon monoxide
- Sulfur dioxide
- Nitrogen dioxide
Using the Air Quality Index
Technical Assistance Document for the Reporting of Daily Air Quality – the Air Quality Index (AQI)