National air-quality statistics · 2020-2024

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 995 monitored counties distribute across the AQI scale.

995
Counties monitored
39
National median AQI
74.3%
Days rated Good

The national picture

Across 995 EPA-monitored U.S. counties, the typical day lands at a good median AQI of 39, and 74.3% of all monitored days fall in the Good band — but 72 counties still clear Good on fewer than half their days.

39
national median AQI · Good
74.3%
of monitored days rated Good
576
counties ≥75% Good days
72
counties <50% Good days

Cleanest: Kenai Peninsula County, Alaska (100.0%). Most polluted: Maricopa County, Arizona (9.0%).

Key figures

Counties monitored

995

Metro areas (CBSAs)

501

States & territories

53

National median AQI

39

Good

Days rated Good

74.3%

244,337 of 328,800 monitored days

Unhealthy-or-worse days

732

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. 1 Hawaii 98.4%
  2. 2 Maine 90.2%
  3. 3 Alaska 89.3%
  4. 4 Vermont 88.9%
  5. 5 Rhode Island 87.1%
  6. 6 New Hampshire 87%
  7. 7 Virginia 86.8%
  8. 8 Massachusetts 85.8%
  9. 9 Puerto Rico 85.7%
  10. 10 Washington 85.4%

Avg Good days · EPA Air Quality System (AQS), 2024

Using these statistics

National averages set the baseline; your county is what you actually breathe.

  • 74.3% 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 995 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, 2020-2024.

Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), 2020-2024 U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), 2020-2024