Annual EPA record

Air Quality History by Year: US Annual EPA AQI Trends, 2020–2025

A historical view of annual EPA Air Quality System summaries, not a current-air report. It compares the unweighted Good-day share across monitored counties. For current conditions and alerts, use AirNow.

Latest annual record 76% Good-day share in 2025

What these annual summaries show

  • 1.The county-average Good-day share was 77.7% in 2020 and 76% in 2025, a -1.7 percentage-point difference.
  • 2.The lowest value in this six-year series was 69.6% in 2023; it is an annual aggregate, not a measure of any one event or cause.
  • 3.The highest value was 77.7% in 2020. Use the county and metro profiles to see how individual places differ from the national county average.

National Good-day share by year

Unweighted average county share of monitored days rated Good (AQI 0–50)

  1. 1 2020 77.7%
  2. 2 2021 72%
  3. 3 2022 75.1%
  4. 4 2023 69.6%
  5. 5 2024 75.4%
  6. 6 2025 76%

Good-day share · EPA Air Quality System, county_trends 2020–2025

EPA Air Quality System (AQS), annual county summaries 2020–2025. This descriptive series does not assign causes to year-to-year changes.

Release-to-release report

What changed in the retained 2020-2025 county record

-1.3pp average county change

Among 864 counties monitored at least 200 days in both endpoint years, 303 recorded a Good-day share at least one percentage point higher and 488 recorded a share at least one point lower. The average county change was -1.3 percentage points.

These are descriptive comparisons of two annual EPA releases, not an attribution of cause or a current-air forecast. Review the adjacent-release change report, the county improvement ranking, the county decline ranking, or compare two places directly with the county comparison tool.

Two change rankings, 2020-2025

According to the 2020-2025 EPA AQS county pair on PlainAirData (864 counties monitored at least 200 days in both years), Solano County, California is #1 of 864 by Good-day share gain (+49.2pp, 50.0% to 99.2%) at median-AQI-drop #7 (+18) ≠ Maricopa County, Arizona #1 by median AQI drop (+39, 112 to 73) at Good-day-share gain #179 (+5.8pp).

+49.2pp
Good-day share gain #1 · Solano Co.
#7
Solano median-AQI drop rank
+39
median AQI drop #1 · Maricopa Co.
#179
Maricopa Good-day share gain rank

Maricopa County's median AQI drop is not a Good-day share lead: 8.8% of monitored days were still rated Good in 2025. A share gain and a median drop are different ledgers on the same retained pair.

Largest Good-day share gains, 2020-2025

Percentage-point change among counties monitored at least 200 days in both years

  1. 1 Solano, California 49.2pp
  2. 2 Montgomery, Alabama 44.4pp
  3. 3 Mono, California 40.1pp
  4. 4 Missoula, Montana 39.3pp
  5. 5 Scotts Bluff, Nebraska 34.6pp
  6. 6 Mariposa, California 27.3pp
  7. 7 Polk, Florida 26.5pp
  8. 8 Calaveras, California 25.6pp
  9. 9 Glenn, California 25.1pp
  10. 10 Escambia, Florida 24.8pp

Good-day share change · EPA Air Quality System, county_trends pair

Largest median AQI drops, 2020-2025

Points of median AQI decline (higher bar = larger drop); not a second share ranking

  1. 1 Maricopa, Arizona 39
  2. 2 Uinta, Wyoming 31
  3. 3 Navajo, Arizona 30
  4. 4 Mono, California 30
  5. 5 Sonoma, California 27
  6. 6 Ponce, Puerto Rico 20
  7. 7 Solano, California 18
  8. 8 Gallatin, Montana 18
  9. 9 Lemhi, Idaho 17
  10. 10 Phillips, Montana 17

Median AQI drop · EPA Air Quality System, county_trends pair

Cleanest states by Good-day share

Latest annual share of Good air days

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

Good-day share · EPA Air Quality System

States with the highest average AQI

Latest annual median AQI; higher values indicate worse annual conditions

  1. 1 California 46
  2. 2 District of Columbia 45
  3. 3 Arizona 45
  4. 4 Arkansas 45
  5. 5 Georgia 43
  6. 6 Oklahoma 43
  7. 7 Ohio 43
  8. 8 South Carolina 43
  9. 9 Iowa 42
  10. 10 Utah 42

Avg median AQI · EPA Air Quality System

EPA Air Quality System (AQS) annual county summaries, 2025. State figures aggregate every monitored county within the state.

How to read this annual history

Each point is built from county-level EPA annual summaries. The chart averages county percentages equally, so it describes the typical monitored county in this dataset rather than a population-weighted national exposure estimate. A county can also change because its monitoring coverage or weather differs from the prior year.

The series is useful for comparing annual records, but it cannot establish why a change occurred. It does not replace a current-air alert, a source-specific pollution analysis, or a health assessment.

Use a county profile or metro profile to compare the underlying annual records for a particular geography. The data source uses CBSA geography for metro records, so metro results are not labelled as city measurements.

Compare change directly

The county improvement ranking compares Good-day share in 2020 and 2025, with a 200-monitored-day floor in both years. That avoids treating a simple change in the number of monitored days as an air-quality improvement.

A change in this ranking is a descriptive difference between the two annual records. It is not a finding about the cause of the change, a forecast, or a current-condition rating.

Data source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), annual summary files (2020-2025).

Data vintage: 2025 is the most recent complete annual record in this series.

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.