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.

Compiled by PlainAirData, Independent data publisher · August 4, 2026

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

Counties monitored

1,002

Metro areas (CBSAs)

504

States & territories

National median AQI

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

State average of its counties' share of EPA-monitored days rated Good (AQI 0–50)

1 Hawaii 93.8%
2 Maine 87%
3 Virginia 86.5%
4 Montana 85.9%
5 Wyoming 85.1%
6 Nebraska 85%
7 New Hampshire 84.9%
8 Alaska 84.4%
9 Puerto Rico 84%
10 Vermont 83.8%

Avg Good days · EPA Air Quality System (AQS), 2025

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.

Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), 2020-2025 U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), 2020-2025