How to Track Outdoor Air Quality—and What the Numbers Actually Mean

Outdoor air isn't automatically clean air. Wildfire smoke, prescribed burns, ozone from summer smog, and urban pollution can make the air outside worse than the air inside your home. Fine particulate matter (PM2.5, tiny particles small enough to get deep into lungs) and ozone are linked to asthma, heart problems, and other health issues with repeated exposure. Pollen adds to the mix for many people each year.

The good news is that a lot of this can be kept out of your house. A tightly sealed building, good filtration, and a properly designed ventilation system all help cut down on what gets inside when outdoor conditions turn bad. The question is knowing when conditions actually warrant closing windows, running an air purifier, or skipping outdoor plans.

The EPA's AirNow app and website (airnow.gov) track real-time outdoor air quality, including smoke and ozone levels, and can help answer that question. The program dates back to 1998, built through a partnership between the EPA, NOAA, the National Park Service, NASA, the CDC, and state and local air agencies, with its roots in the 1970 Clean Air Act, which required the EPA to set air-quality standards and alert the public when pollution gets unhealthy. Ground-level ozone, a major cause of summer smog, is one of the pollutants it tracks. Checking a tool like this alongside the weather forecast is becoming as routine as checking for rain, especially if wildfire smoke or ozone alerts are common where you live.