0-50: Good

Air quality considered satisfactory; air pollution poses little or no risk.

Source: airnow.gov

51-100: Moderate

Air quality acceptable; however, some pollutants may pose a moderate health concern for a small number of people who are unusually sensitive to air pollution.

Source: airnow.gov

101-150: Unhealthy for Sensitive Groups

Children, people who are sensitive to ozone, and people with heart or lung disease may experience health effects. General public is unlikely to be affected.

Source: airnow.gov

151-200: Unhealthy

Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.

Source: airnow.gov

201-300: Very Unhealthy

Health alert: Everyone may experience more serious health effects. Most people should restrict outdoor exertion to morning or late evening hours.

Source: airnow.gov

301-500: Hazardous

Health warnings of emergency conditions. The entire population is more likely to be affected. Everyone should avoid outdoor exertion.

Source: airnow.gov