The air quality map
Every county in the lower 48, from CDC's daily estimates for 2001 to 2022. See which months bring bad air, how it has changed, and whether it's smoke or smog. Tap a county for its full picture.
Loading the map…
Biggest changes since the early 2000s
Counties of 250,000 people or more. Bad-air days a year, 2001 to 2005 compared with 2018 to 2022. The tag says what drove most of the change: fine particles (in the West, mostly wildfire smoke) or ozone.
Most improved
Getting worse
About this map
The colors come from the CDC's Environmental Public Health Tracking Network, which estimates daily fine particles (PM2.5) and ozone for every county from monitors, satellites and weather models. We count a day as bad when the worst spot in a county goes over 35.4 µg/m³ of fine particles or 70 ppb of ozone, the levels where the AQI passes 100. That matches how the EPA counts a county by its worst monitor. The model ends in 2022, so the 2023 Canadian smoke isn't here yet, and it doesn't include Alaska or Hawaii.
County pages use the EPA's monitor readings, which run through 2025. For most counties the two line up. In a few, such as Maricopa County in Arizona, the model estimates far fewer ozone days than the monitors recorded. Where they differ, the monitor number is the one to trust, because it's a measurement.