What to Do When Air Quality Is Bad: AQI Guide and Safety Tips

The air around you carries more than oxygen. On any given day, it may also hold wildfire smoke from thousands of miles away, dust blown across the Atlantic from the Sahara, ground-level ozone cooked by summer heat, and pollen thick enough to coat your windshield. When those particles reach high enough concentrations, breathing becomes work for your body. The Air Quality Index was built to tell you when that threshold is being crossed and how seriously.

How the AQI Scale Works

The Air Quality Index runs from 0 to 500. Lower numbers mean cleaner air. The scale is divided into six color-coded categories: Good (0 to 50), Moderate (51 to 100), Unhealthy for Sensitive Groups (101 to 150), Unhealthy (151 to 200), Very Unhealthy (201 to 300), and Hazardous (301 and above). AQI readings are calculated from five major pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide.

According to AirNow, the EPA-operated service providing real-time air quality data, most healthy adults can go about normal activity at Moderate levels with minimal concern. The calculus shifts at 100, where people with heart or lung disease, older adults, and children should begin reducing prolonged outdoor exertion.