The Air Quality Index (AQI) is the EPA's 0–500 scale for communicating air pollution levels. Use this reference to understand what your local AQI reading means for your health and activity decisions.
AQI Level Lookup
How to Read the Air Quality Index
The AQI reference helps you interpret air quality readings and take appropriate action. The AQI uses a 0-500 scale where higher numbers mean more pollution and greater health risk. Each level has a color code (green through maroon) and health guidance for the general public and sensitive groups.
Sensitive Groups
Sensitive populations include children, older adults, and people with heart or lung conditions (asthma, COPD, heart disease). These groups are affected at lower AQI levels than healthy adults. When AQI exceeds 100, sensitive groups should reduce prolonged outdoor exertion.
Wildfire Smoke
During wildfire events, AQI can spike into Unhealthy (151+) or Hazardous (301+) territory rapidly. N95 masks significantly reduce PM2.5 inhalation; cloth and surgical masks offer much less protection. Indoor air purifiers with HEPA filters are effective for reducing indoor PM2.5 during smoke events. Keep windows and doors closed.
For a detailed walkthrough, see our guide: Exercising During Poor Air Quality.
FAQ
Is this AQI reference free?
Yes, completely free with no signup. Reference the complete AQI scale and health guidance instantly.
What is the Air Quality Index (AQI)?
The AQI is a 0-500 scale used by the EPA to communicate how clean or polluted outdoor air is. It tracks five major pollutants: ground-level ozone, particle pollution (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. The daily AQI reflects the worst of these pollutant readings.
What AQI is considered safe?
AQI 0-50 (Green) is 'Good' — little to no health risk. AQI 51-100 (Yellow) is 'Moderate' — acceptable for most people; sensitive individuals may experience minor effects. Above 100, the EPA recommends that at-risk groups (children, elderly, those with respiratory conditions) limit outdoor activity.
What is PM2.5 and why is it dangerous?
PM2.5 refers to fine particulate matter with a diameter of 2.5 micrometers or less — small enough to penetrate deep into lung tissue and enter the bloodstream. PM2.5 from wildfires, vehicle exhaust, and industrial emissions is linked to heart attacks, strokes, lung cancer, and respiratory disease with prolonged exposure.
How can I check real-time AQI?
Check AirNow.gov (official EPA source), IQAir.com, PurpleAir.com (hyperlocal sensors), or your weather app. Many cities have multiple monitoring stations — check one near your location. During wildfire events, AQI can vary significantly within a few miles.