The Air Quality Index (AQI) is your daily guide to understanding how clean or polluted the air is in your area. Developed by the Environmental Protection Agency (EPA), this standardized measurement system helps you make informed decisions about outdoor activities and when to take precautions.
Understanding the AQI Scale
The AQI runs from 0 to 500, divided into six color-coded categories:
Good (0-50) – Green
Air quality is satisfactory, and air pollution poses little or no risk. This is the ideal time for outdoor activities, including exercise and sports.
Moderate (51-100) – Yellow
Air quality is acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution. Most people can continue normal activities.
Unhealthy for Sensitive Groups (101-150) – Orange
Members of sensitive groups—including children, older adults, and people with respiratory or heart conditions—may experience health effects. The general public is less likely to be affected at this level.
Unhealthy (151-200) – Red
Everyone may begin to experience health effects at this level. Members of sensitive groups may experience more serious effects. Consider reducing prolonged outdoor exertion.
Very Unhealthy (201-300) – Purple
This triggers a health alert, meaning everyone may experience more serious health effects. Avoid prolonged outdoor activities and consider running air purifiers indoors.
Hazardous (301-500) – Maroon
Health warnings of emergency conditions. The entire population is more likely to be affected. Stay indoors with air purification running continuously.
What Pollutants Does AQI Measure?
The AQI tracks five major air pollutants regulated by the Clean Air Act:
- Ground-level ozone (O3) – Formed when pollutants react with sunlight
- Particulate matter (PM2.5 and PM10) – Tiny particles from dust, smoke, and emissions
- Carbon monoxide (CO) – Colorless, odorless gas from combustion
- Sulfur dioxide (SO2) – From burning fossil fuels
- Nitrogen dioxide (NO2) – From vehicle emissions and power plants
How to Check Your Local AQI
Several reliable sources provide real-time AQI data:
- AirNow.gov (EPA’s official air quality website)
- IQAir’s World Air Quality Map
- Weather apps on your smartphone
- Local news weather segments
Taking Action Based on AQI
When AQI rises above 100, consider these protective measures:
- Limit outdoor exercise to early morning when pollution is typically lower
- Keep windows and doors closed
- Run HEPA air purifiers to clean indoor air
- Check forecasts before planning outdoor events
Understanding the AQI empowers you to protect your family’s health. By monitoring daily readings and taking appropriate precautions, you can minimize your exposure to harmful air pollution.
Sources
- U.S. Environmental Protection Agency. “Air Quality Index (AQI) Basics.” EPA.gov
- American Lung Association. “State of the Air Report 2024.”
- World Health Organization. “Air Quality Guidelines.” WHO.int