The Air Quality Index (AQI) is a standardized scale developed by the EPA to communicate how clean or polluted the air is — and what health effects might be of concern. The scale runs from 0 to 500, and the higher the AQI value, the greater the level of air pollution and the greater the health concern.
How AQI Is Calculated
The AQI is calculated based on concentrations of five major air pollutants regulated by the Clean Air Act:
- Ground-level ozone
- Particle pollution (PM2.5 and PM10)
- Carbon monoxide (CO)
- Sulfur dioxide (SO2)
- Nitrogen dioxide (NO2)
Each pollutant has its own AQI calculation. The overall AQI for a location is the highest individual pollutant AQI at that time — meaning if PM2.5 is at 120 and ozone is at 75, the AQI reported is 120.
AQI Categories
| AQI Range | Category | Color | Who's Affected |
|-----------|----------|-------|----------------|
| 0–50 | Good | Green | No health concern |
| 51–100 | Moderate | Yellow | Unusually sensitive people |
| 101–150 | Unhealthy for Sensitive Groups | Orange | People with lung/heart disease, elderly, children |
| 151–200 | Unhealthy | Red | Everyone may begin to experience effects |
| 201–300 | Very Unhealthy | Purple | Health alert — serious effects for everyone |
| 301–500 | Hazardous | Maroon | Emergency conditions — everyone affected |
What Should You Do at Each Level?
Good (0–50): Air quality is satisfactory. Enjoy outdoor activities.
Moderate (51–100): Air quality is acceptable. Unusually sensitive people should consider limiting prolonged outdoor exertion.
Unhealthy for Sensitive Groups (101–150): Reduce prolonged or heavy exertion if you have heart or lung disease. Children and elderly should limit time outdoors.
Unhealthy (151–200): Everyone should reduce prolonged outdoor exertion. People in sensitive groups should avoid outdoor activity.
Very Unhealthy (201–300): Everyone should avoid prolonged outdoor exertion. Sensitive groups should remain indoors.
Hazardous (301+): Everyone should avoid all outdoor exertion and stay indoors with windows closed.
How to Check Your AQI
You can check your local AQI on LocalAirData by searching for your city or ZIP code. We pull real-time data from the EPA's AirNow network, updated hourly.