Understanding the Air Quality Index (AQI) Categories
The Air Quality Index (AQI) is a standardized system developed by the U.S. Environmental Protection Agency (EPA) to communicate daily air quality levels to the public. It translates concentrations of common air pollutants into a scale from 0 to 500, where higher values indicate greater pollution and potential health risks. (airnow.gov)
What Are the AQI Categories?
The AQI is divided into six color-coded categories, each representing a different level of health concern:
- Good (0–50): Air quality is satisfactory, posing little or no risk.
- Moderate (51–100): Air quality is acceptable; however, there may be a risk for some individuals sensitive to air pollution.
- Unhealthy for Sensitive Groups (101–150): Sensitive individuals may experience health effects; the general public is less likely to be affected.
- Unhealthy (151–200): Some members of the general public may experience health effects; sensitive groups may experience more serious effects.
- Very Unhealthy (201–300): Health alert: everyone may experience more serious health effects.
- Hazardous (301 and higher): Health warning of emergency conditions: everyone is more likely to be affected.
Each category is associated with a specific color to facilitate quick recognition:
- Green: Good
- Yellow: Moderate
- Orange: Unhealthy for Sensitive Groups
- Red: Unhealthy
- Purple: Very Unhealthy
- Maroon: Hazardous
(epa.gov)
How Is the AQI Calculated?
The AQI is calculated for five major pollutants regulated by the Clean Air Act:
- Ground-level ozone
- Particulate matter (PM₂.₅ and PM₁₀)
- Carbon monoxide
- Sulfur dioxide
- Nitrogen dioxide
Each pollutant has its own AQI scale, and the highest AQI value among these pollutants determines the overall AQI for a location. For example, if ozone has an AQI of 120 and PM₂.₅ has an AQI of 80, the overall AQI would be 120. (airnow.gov)
Health Implications of AQI Levels
Understanding AQI categories is crucial for protecting your health:
- Good (0–50): Air quality is satisfactory, and air pollution poses little or no risk.
- Moderate (51–100): Air quality is acceptable; however, there may be a risk for some individuals sensitive to air pollution.
- Unhealthy for Sensitive Groups (101–150): Sensitive individuals may experience health effects; the general public is less likely to be affected.
- Unhealthy (151–200): Some members of the general public may experience health effects; sensitive groups may experience more serious effects.
- Very Unhealthy (201–300): Health alert: everyone may experience more serious health effects.
- Hazardous (301 and higher): Health warning of emergency conditions: everyone is more likely to be affected.
Sensitive groups include children, the elderly, and individuals with respiratory or heart conditions. It's advisable for these groups to limit prolonged outdoor exertion when the AQI is in the "Unhealthy for Sensitive Groups" category or higher. (epa.gov)
How to Monitor AQI Levels
Staying informed about local air quality is essential. The EPA provides real-time AQI data through the AirNow website, where you can check current air quality levels in your area. (airnow.gov)
Protecting Your Health
When the AQI indicates unhealthy air quality, consider the following precautions:
- Limit Outdoor Activities: Reduce prolonged or heavy exertion outdoors, especially if you belong to sensitive groups.
- Stay Indoors: Keep windows and doors closed to prevent outdoor air from entering your home.
- Use Air Purifiers: Utilize air purifiers with HEPA filters to reduce indoor air pollution.
- Monitor Health Symptoms: Be alert to any respiratory issues or other health symptoms and seek medical attention if necessary.
By understanding AQI categories and taking appropriate actions, you can safeguard your health and well-being in varying air quality conditions.