Counties Tracked
1,002
EPA AQS active monitors
EPA Air Quality System · 1,002 counties · 2020-2025
How clean is the air
where you live?
AQI summaries, pollutant breakdowns, and good-day trends for 1,002 U.S. counties, 504 metros, and 53 states, direct from EPA AQS.
- Counties monitored
- 1,002
- Metro areas
- 504
- States covered
- 53
- Years of data
- 2020-2025
- Good · 242,174 d · 74.9%
- Moderate · 77,983 d · 24.1%
- USG · 2,452 d · 0.8%
- Unhealthy · 577 d · 0.2%
- Very Unhealthy · 49 d · 0.0%
- Hazardous · 53 d · 0.0%
The national picture
Across 1,002 monitored U.S. counties, the typical county's median day lands at AQI 39 - inside the Good band, but the most-polluted 10% of counties average AQI 54, 3.1x higher than the cleanest 10% at AQI 17, yet only 75% of the 323,288 monitored days clear the Good threshold nationwide.
- 39
- median AQI in the typical monitored county
- 74.9%
- of monitored days rated Good
- 3.1x
- dirtiest-decile vs cleanest-decile AQI gap
- 1,002
- counties with an active EPA monitor
Cleanest typical air sits in Karnes, Texas; the lowest annual Good-day share belongs to Maricopa, Arizona.
Metro Areas
504
MSA-level aggregation
Typical County AQI
38.5
Good · mean of the 977 county medians
Good Days
74.9%
Share of monitored days at AQI ≤50
4.9pp vs 70% benchmark
According to the U.S. Environmental Protection Agency's Air Quality System, PlainAirData compiles more than 5,971 county-year air quality records spanning 2020 through 2025, last refreshed in July 2026; see our methodology for the full source list.
National good-day share 74.9%
Illustrative reference (not an official EPA target)
242,174 of 323,288 monitored days nationwide fell in the Good band (AQI 0-50), counting every monitored day once rather than every county once. NAAQS attainment is a pollutant-concentration standard, not a percent-of-days target; 85% is shown here only as an illustrative reference point, not an official EPA benchmark.
Coverage of US counties 31.9%
Target
1,002 of 3,144 U.S. counties have an active EPA AQS monitor.
Cleanest and most-polluted counties
View all rankings →Cleanest air by typical AQI
Largest share of days outside the Good band
How EPA monitoring is distributed
Air-quality data isn't uniform, counties with denser monitoring networks (urban, attainment-classified, or industrial) feed more readings into the AQS database than rural counties. This grid shows where EPA AQS monitors actively report, color-encoded by the share of monitored days that fell in the Good band (AQI 0-50). Sparse coverage is itself a finding: 2,200+ U.S. counties have no active monitor, and what we don't measure, we cannot regulate.
States by Air Quality
View all Scale: 60.7%–67.3% 67.3%–73.9% 73.9%–80.6% 80.6%–87.2% 87.2%–93.8%
Cleanest states right now
Hawaii
93.8%3 counties · typical county AQI 27
Maine
87.0%11 counties · typical county AQI 35
Virginia
86.5%30 counties · typical county AQI 34
Montana
85.9%23 counties · typical county AQI 25
Wyoming
85.1%17 counties · typical county AQI 31
Nebraska
85.0%11 counties · typical county AQI 32
New Hampshire
84.9%7 counties · typical county AQI 37
Alaska
84.4%8 counties · typical county AQI 20
Puerto Rico
84.0%8 counties · typical county AQI 22
Vermont
83.8%4 counties · typical county AQI 32
Explore More
Air Quality Guides
Learn how to read and use air quality data from official EPA sources.
Understanding the AQI
What each level means and when to limit outdoor activity.
5 Common Air Pollutants
Ozone, PM2.5, PM10, NO₂, and CO, where they come from and why they matter.
Best & Worst Air Quality
Which US counties have the cleanest and most polluted air.
Best & Worst City Air
Metro rankings and what drives urban air quality.
Air Pollution & Health
Health effects and who is most at risk.
Frequently Asked Questions
What data does PlainAirData provide?
PlainAirData provides EPA Air Quality System data including annual AQI values for 1002 counties, 504 metros, and 50 states + DC + US territories (53 jurisdictions) from 2020-2025.
What is the Air Quality Index?
The AQI is a standardized measure from 0-500 that indicates how clean or polluted the air is. Values below 50 are considered good, while values above 100 may be unhealthy.
Where does PlainAirData data come from?
All data comes from the EPA Air Quality System, the official repository of ambient air quality monitoring data from state and local agencies.
Research
Original analysis from PlainAirData, every statistic derived from our own database. See all research.
Research
Top 10 US Counties with Most Unhealthy Days in 2024
Explore the 10 counties like Rio Blanco, Colorado, with up to 88 unhealthy days in 2024, based on EPA AQS data for 1002 counties, revealing key AQI trends and pollutant impacts on public health.
ResearchState Averages of Median AQI Across 2020-2024 in 53 US States
Discover how 50 states + DC + US territories (53 jurisdictions) like Alabama, whose counties averaged a median AQI of 41.1 across the window, trended from 2020 to 2024 using EPA data, including pollutant days for ozone and PM2.5, affecting over 1002 counties.
ResearchNational Trends in Good Days Percentage from 2020 to 2024
Analyze nationwide good days trends across 1002 counties and 504 metros, with Alabama at 70.0% of its monitored days rated Good across 2020-2025 and Alaska at 85.7%, drawn from EPA AQS data on AQI metrics.
About this data
How PlainAirData works, and why you can trust these numbers
What this site is
PlainAirData turns the U.S. EPA's Air Quality System (AQS) annual county and metro summary files into readable air-quality profiles for 1,002 counties, 53 states, and every monitored U.S. metro area. Every figure traces back to an EPA-published dataset, never a third-party estimate.
Editorial process
- Source. Download the EPA AQS Annual AQI by County and by CBSA summary files directly from aqs.epa.gov, 2020-2025.
- Verify. Each county and state figure is validated against the source release before publication, and re-checked whenever EPA publishes a new annual file.
- Publish. Compile per-county, per-state, and per-metro profiles with the underlying dataset and vintage documented on the methodology page.
Editorial independence & corrections
PlainAirData does not accept payment, sponsorship, or promoted placement from government agencies, environmental organizations, or any other covered entity. Found an error? Contact us via the contact page. See our methodology for full source attribution.
Frequently asked
Where does PlainAirData's air quality data come from?
Every figure comes from the U.S. EPA's Air Quality System (AQS), the same federal database used for regulatory reporting. We do not run our own monitors or estimate values.
Is this real-time air quality data?
No. PlainAirData shows historical annual summaries (2020-2025), not current conditions. For today's AQI, see EPA AirNow.
Is PlainAirData affiliated with the EPA?
No. PlainAirData is an independent data portal. We present publicly available federal data in a more accessible format but are not affiliated with the U.S. EPA or any government agency.
Every figure on PlainAirData is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This homepage summarizes EPA AQS data aggregated across every monitored county, metro, and state. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2025.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.