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

Building Science

The EPA’s AirNow app can help you track wildfire smoke, ozone, and other pollutants—and decide when it might be time to take action

A decade ago, most of us never thought about checking the outdoor air quality before opening the windows. We checked the weather forecast for rain, wind, or temperature—but not the air we were about to breathe. Today, wildfire smoke, prescribed burns, ozone alerts, and urban pollution have made outdoor air quality another environmental condition worth tracking. And there’s an app for that.

We often think of outdoor air as “fresh air,” but that’s not always true. Smoke, fine particulate matter (PM2.5), ozone, and other pollutants can make outdoor air more hazardous than the air inside a home. Pollen affects millions of people each year, and repeated exposure to poor air quality has been linked to asthma, cardiovascular disease, and other chronic health problems.

Fortunately, many of these pollutants can be filtered before they become part of your indoor environment. It starts with controlling the air that enters the home. A tight building enclosure, effective filtration, and a properly designed ventilation system can all help reduce our exposure when outdoor air gets bad.

But how do you know when it’s time to close the windows, turn on the air purifier, or avoid outdoor activities? That’s where the EPA’s AirNow app comes in.

A brief history of AirNow

AirNow got its start in 1998 as a partnership between the EPA, NOAA, the National Park Service (NPS), NASA, the CDC, and state, tribal, and local air-quality agencies. Its original purpose was to provide near-real-time information about ground-level ozone. The roots of the program go back to the Clean Air Act of 1970, which required the EPA to establish national air-quality standards and let the public know when pollution reached unhealthy levels.

Ground-level ozone—one of the primary pollutants responsible for summertime smog—is formed when nitrogen oxides (NOₓ) and volatile organic…