How to Read the Air Quality Index and What the Numbers Mean

Understanding the Air Quality Index

The Air Quality Index translates complex pollution measurements into a simple number. Values run from 0 (clean air) to 500 (don’t go outside). The reading combines data on PM2.5, ozone, carbon monoxide, and other pollutants into one overall score.

What the Numbers Mean

0-50 is good—breathe easy. 51-100 is moderate, fine for most people. 101-150 starts affecting sensitive groups. 151-200 is unhealthy for everyone. Above 200 means stay indoors if you can.

Where to Check

AirNow.gov gives real-time AQI data for any location. Most weather apps include air quality in their forecasts. Purple Air runs community sensor networks that often provide more local detail. Check before planning outdoor activities.

When the Numbers Are High

High AQI days mean staying inside when possible. HEPA purifiers clean indoor air. N95 masks filter fine particles if you need to be outside. Keep windows closed when readings climb—that fresh air isn’t so fresh.