Air Quality Index

The Air Quality Index, or AQI, is an index for reporting daily air quality. It tells you how clean or polluted the air is in your region.

The U.S. Environmental Protection Agency (EPA) has developed the index, which is divided into 6 categories, indicating increasing levels of health concern.

Air Quality is based on 5 pollutants regulated by the Clean Air Act:
  • Carbon monoxide
  • Ground-level ozone
  • Nitrogen dioxide
  • Particulate matter
  • Sulfur dioxide
Each pollutant has established standards which are evaluated to determine the daily AQI. An AQI value over 300 represents hazardous air quality, whereas if the value is below 50 the air quality is good.

Understanding AQI colors
Specific colors are assigned to each AQI category to make it easier for people to quickly determine whether air pollution is reaching unhealthy levels in their community.

Air Quality Index Colors
Health Concern Level
Numerical Value
0 - 50
Air quality is considered satisfactory, and air pollution poses little or no risk.
Moderate 51 - 100
Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.
Unhealthy for Sensitive Groups
101 - 150
Members of sensitive groups may experience health effects. The general public is not likely to be affected.
Unhealthy 151 - 200
Everyone may begin to experience health effects, members of sensitive groups may experience more serious health effects.
Very Unhealthy
201 - 300
Health Alert: everyone may experience more serious health effects.
Hazardous 301 - 500
Health warnings of emergency conditions. The entire population is more likely to be affected.