Compare air quality between counties
Put up to 3 counties side by side. The big number is bad-air days a year, from EPA monitors where the county has them. Each ring shows which months bring bad air, and the strip under it shows every year from 2001 to 2022.
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Add a county from the map
Shading is CDC's estimate of bad-air days a year, 2018 to 2022. The numbered dots are the counties above. Click any county to add it. The address bar keeps your list, so you can share it.
How to read a ring
Each of the 12 slices is a month, starting with January at the top and going clockwise. The longer the slice, the more bad-air days that month averaged from 2001 to 2022, from CDC estimates. The striped brown part is smoke and particles; the blue part outside it is ozone.
The big number above each ring is bad-air days a year. Where a county has EPA monitors, it's their count for 2021 to 2025, which includes the 2023 Canadian smoke. Where it doesn't, it's CDC's estimate for 2018 to 2022. When the two differ a lot, trust the monitors: they measure the air directly.
A ring that bulges at the bottom has a summer problem, usually ozone in the South and East or smoke in the West. A ring that bulges at the top has a winter problem, usually smoke from wood stoves trapped by cold, still air.
Questions people ask about comparing places
How do I compare air quality between two cities?
Add each city's county with the search box. The rings show which months bring bad air in each, and the strips show how they changed from 2001 to 2022. Each county also has its own page with EPA monitor data.
Why compare counties and not cities?
The CDC's estimates and the EPA's daily summaries are both reported by county. A big city can span several counties, so add each one you're considering.
These maps use the CDC Environmental Public Health Tracking Network's daily estimates of fine particles (PM2.5) and ozone for every county in the lower 48, 2001 to 2022. A bad-air day is a day when the worst spot in a county goes over 35.4 µg/m³ of fine particles or 70 ppb of ozone, where the AQI passes 100. How we count · Download the data