California Wildfire Smoke

The U.S. Environmental Protection Agency’s AirNow website displays air quality with its “air quality index,” or AQI. On a scale from 0 to 500, the index is divided into six categories: good, moderate, unhealthy for sensitive groups, unhealthy, very unhealthy and hazardous. The readings are based on measurements of five kinds of pollution tracked by the EPA, including ozone and particulate matter.

In this case, the AQI readings reflect the density of fine particulate matter in the air full of wildfire smoke.

On this scale, readings above 100 mean the air is unhealthy for sensitive groups, including people with heart or lung disease, older people and children. Readings above 150 are considered unhealthy for everyone.

For more, read Harriet Rowan’s coverage.