An AQI of 100 or below is generally satisfactory. Above 100, air is unhealthy for sensitive groups first, then for everyone as the value rises.
| Color | Level of concern | AQI values |
|---|---|---|
| Green | Good | 0 to 50 |
| Yellow | Moderate | 51 to 100 |
| Orange | Unhealthy for Sensitive Groups | 101 to 150 |
| Red | Unhealthy | 151 to 200 |
| Purple | Very Unhealthy | 201 to 300 |
| Maroon | Hazardous | 301 and higher |
What an air quality alert means
An air quality alert is an irregular notice about air pollution conditions. State and local agencies create these notices, and the National Weather Service passes them along to the public. Use the AQI colors and numbers on this page to read how serious the air is where you are.
What each AQI color means
Green, Good (0 to 50): air quality is satisfactory, with little or no risk. Yellow, Moderate (51 to 100): acceptable, with some risk for unusually sensitive people. Orange, Unhealthy for Sensitive Groups (101 to 150): sensitive groups may be affected, and the general public is less likely to be. Red, Unhealthy (151 to 200): some of the general public may be affected, and sensitive groups may face more serious effects. Purple, Very Unhealthy (201 to 300): a health alert, with increased risk for everyone. Maroon, Hazardous (301 and higher): emergency conditions, and everyone is more likely to be affected.
Which pollutants the AQI covers
The AQI covers five major pollutants regulated under the Clean Air Act: ground-level ozone, particle pollution (including PM2.5 and PM10), carbon monoxide, sulfur dioxide and nitrogen dioxide. For each pollutant an AQI of 100 generally corresponds to the short-term national air quality standard set to protect public health.
How it works
An AQI value of 100 generally corresponds to the short-term national air quality standard for protecting public health. Values at or below 100 are generally thought of as satisfactory.
Who is affected
At Unhealthy for Sensitive Groups, members of sensitive groups may experience health effects and the general public is less likely to be affected. At Unhealthy, some members of the general public may feel effects. At Very Unhealthy the risk is increased for everyone, and Hazardous is a health warning of emergency conditions.
Where to look
AirNow publishes Activity Guides that explain how to protect your health when the AQI reaches unhealthy levels. For smoke at home, see our wildfire guide.
Check your own location
See current official alerts and the impact for your ZIP code.
Common questions
What does an air quality alert mean?
An air quality alert is an irregular notice about air pollution conditions. State and local agencies create these notices and the National Weather Service passes them along to the public.
Who issues an air quality alert?
State and local agencies create air quality alerts. The National Weather Service passes them along to the public.
What AQI number is unhealthy?
Above 100. Air quality is unhealthy first for sensitive groups (101 to 150), then for some of the general public (Unhealthy, 151 to 200), and for everyone at Very Unhealthy (201 to 300) and Hazardous (301 and higher).
What is a hazardous AQI?
An AQI of 301 or higher is Hazardous, shown in maroon. AirNow describes it as emergency conditions in which everyone is more likely to be affected.
What do the AQI colors mean?
Green is Good (0 to 50), yellow is Moderate (51 to 100), orange is Unhealthy for Sensitive Groups (101 to 150), red is Unhealthy (151 to 200), purple is Very Unhealthy (201 to 300) and maroon is Hazardous (301 and higher).
Which pollutants does the AQI measure?
Five major pollutants regulated under the Clean Air Act: ground-level ozone, particle pollution (PM2.5 and PM10), carbon monoxide, sulfur dioxide and nitrogen dioxide.
Sources
Reviewed by the Storm Incoming editorial team on October 26, 2026. Follow local emergency officials if their instructions differ.