Air Quality by State

AQI above 150 is considered unhealthy for everyone. Above 200 is Very Unhealthy — sensitive groups should stay indoors and everyone should limit outdoor exertion. Above 300 is Hazardous — everyone should stay indoors. The 2020 California wildfires caused AQI readings above 500 in some areas, off the standard scale.

California consistently has the most counties with poor air quality days, particularly in the San Joaquin Valley (Fresno, Bakersfield) and Los Angeles. Other states with frequent high AQI include Arizona (dust storms), Pennsylvania (industrial), and states prone to wildfire smoke (Oregon, Washington, Idaho, Montana).

Yes. At AQI 150+, sensitive individuals (asthmatics, elderly, children) may experience symptoms within hours. At AQI 200+, even healthy adults can experience throat irritation, coughing, or difficulty breathing. Long-term exposure to moderate pollution (AQI 51-100 daily) is associated with increased cardiovascular and respiratory disease risk.

The US AQI is calculated from six major pollutants: ground-level ozone (O3), particle pollution (PM2.5 and PM10), carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen dioxide (NO2). The AQI reported is the highest value across all measured pollutants. EPA monitoring stations report data every hour.