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Calculate the Air Quality Index (AQI) from pollutant concentrations including PM2.5 (fine particles), PM10, ground-level ozone, nitrogen dioxide, and carbon monoxide. Get AQI category, color code, health effects, and activity recommendations.
The Air Quality Index (AQI) is a 0-500 scale used by the EPA to communicate daily air quality. Values 0-50 are "Good" (green). Values 101-150 are "Unhealthy for Sensitive Groups." Above 200 is "Very Unhealthy." PM2.5 (fine particles smaller than 2.5 micrometers) is the most dangerous air pollutant for human health.
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 you might experience. It runs from 0 to 500 — the higher the AQI value, the greater the level of air pollution and health concern. AQI values at or below 100 are generally considered satisfactory. When AQI values exceed 100, the air quality is considered unhealthy for certain groups.
Six major air pollutants are monitored: ground-level ozone (O3), particle pollution (PM2.5 and PM10), carbon monoxide (CO), nitrogen dioxide (NO2), and sulfur dioxide (SO2). Each pollutant has its own AQI calculation breakpoints established by the EPA based on health research. The overall AQI for a location is the highest AQI value among all measured pollutants.
| AQI Value | Category | Color | Who is Affected |
|---|---|---|---|
| 0-50 | Good | Green | None — air quality is satisfactory |
| 51-100 | Moderate | Yellow | Unusually sensitive people may be affected |
| 101-150 | Unhealthy for Sensitive Groups | Orange | Children, elderly, people with asthma |
| 151-200 | Unhealthy | Red | Everyone may begin to experience effects |
| 201-300 | Very Unhealthy | Purple | Health alert — everyone may experience serious effects |
| 301-500 | Hazardous | Maroon | Emergency conditions — everyone affected |
Fine particulate matter (PM2.5) — particles smaller than 2.5 micrometers (about 1/30th the width of a human hair) — are the most harmful air pollutant for human health. These ultra-fine particles penetrate deep into the lungs and can enter the bloodstream. Long-term exposure increases risk of heart disease, stroke, lung cancer, and premature death. Short-term exposure at high concentrations causes respiratory symptoms, asthma attacks, and aggravated cardiovascular disease.
| Source | Pollutants | Location/Season |
|---|---|---|
| Vehicle exhaust | PM2.5, NO2, CO | Urban areas, near highways |
| Industrial emissions | SO2, PM2.5, NOx | Near factories, power plants |
| Wildfires | PM2.5, CO | Seasonal, large geographic impact |
| Agricultural burning | PM2.5, CO | Rural areas, seasonal |
| Construction dust | PM10 | Urban development zones |
| Coal combustion | SO2, PM2.5, Mercury | Power plants, winter heating |
When AQI exceeds 100 (Orange): sensitive groups should limit prolonged outdoor exertion. When AQI exceeds 150 (Red): everyone should limit outdoor activity. When AQI exceeds 200 (Purple): stay indoors with windows closed, use air purifiers (HEPA filter), wear N95 or P100 respirator masks if going outside. AQI above 300 (Maroon): Emergency conditions — remain indoors. Indoor air quality can be 2-5x worse than outdoor air: avoid candles, incense, air fresheners, and tobacco smoke indoors. HEPA air purifiers effectively remove PM2.5 particles.
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