Counties monitored
1,002
National air-quality statistics · 2020-2025
U.S. Air Quality Statistics
The headline figures from the EPA Air Quality System: how clean U.S. air is on average, where it is cleanest and most polluted, and how the 1,002 monitored counties distribute across the AQI scale.
- 1,002
- Counties monitored
- 38.5
- Typical county median AQI
- 74.9%
- Days rated Good
The national picture
Across 1,002 EPA-monitored U.S. counties, the typical county's median day lands at a good AQI of 39, and 74.9% of all monitored days fall in the Good band, but 60 counties still clear Good on fewer than half their days.
- 39
- national median AQI · Good
- 74.9%
- of monitored days rated Good
- 574
- counties ≥75% Good days
- 60
- counties <50% Good days
Cleanest: Kenai Peninsula County, Alaska (100.0%). Most polluted: Maricopa County, Arizona (8.8%).
Key findings
- Across every EPA-monitored U.S. county, 74.9% of all monitored days fell in the Good AQI band (0-50) in the 2025 annual release.
- Kenai Peninsula County, Alaska has the cleanest air of any EPA-monitored U.S. county, with 100.0% of days rated Good.
- Maricopa County, Arizona has the most polluted air of any EPA-monitored U.S. county, with only 8.8% of days rated Good.
- 574 of 1,002 monitored counties (57.3%) clear at least 75% Good-air days.
- 60 monitored counties fall below a 50% Good-day share, meaning air quality misses the Good band more often than not.
- Hawaii is the cleanest of the 52 U.S. states and territories with at least a year of monitoring, with 93.8% of its EPA-monitored days rated Good.
- The median AQI in the typical monitored county is 39 (Good), averaged across 1,002 counties.
- 679 unhealthy-or-worse monitored days (AQI 151+) were recorded across all counties combined in the dataset period.
Key figures
Metro areas (CBSAs)
504
States & territories
53
National median AQI
39
Good
Days rated Good
74.9%
245,771 of 328,003 monitored days
Unhealthy-or-worse days
679
AQI 151+ across all counties
The 10 cleanest states by Good-day share
Cleanest states by average Good-day share
Using these statistics
National averages set the baseline; your county is what you actually breathe.
- 74.9% of monitored days are Good nationally, but the spread is wide, open the rankings to see the full cleanest-to-most-polluted order. Rankings
- Look up any of the 1,002 monitored counties for its median AQI, distribution, and five-year trend. County data
- New to the scale? The guide explains what a national median of 39 means for sensitive groups. Understand AQI
Figures count only days each EPA monitor reported; roughly two thousand U.S. counties have no monitor and are not represented. Data: EPA Air Quality System annual summaries, 2020-2025.
Download the EPA AQS annual county AQI extract cited on this page: annual-aqi-by-county.csv or the JSON distribution (public domain / CC0). Method notes live on /methodology and /data.
Share this annual record
Send the source-year summary or download its ready-to-use data card.
Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), 2020-2025