Air quality tools

Air Quality Tools

Four free, interactive tools built on EPA Air Quality System data, look up, compare, rank, and translate the air quality of any U.S. county.

1,002
Counties covered
4
Interactive tools
74.9%
US good-day share

EPA AQI category stamps

EPA AQI category stamps · monitored-day counts

One dataset, four ways in

Every tool here runs on the same EPA Air Quality System figures behind the county pages, no estimates, no fabrication, across all 1,002 monitored U.S. counties.

Look up
any county AQI and category
Compare
two or three counties side by side
Rank
cleanest counties by state
Translate
an AQI value into health guidance

Today's cleanest is Kenai Peninsula County, Alaska (100.0% Good days); the most polluted, Maricopa County, Arizona (8.8%).

Median AQI ≠ good-day share

According to EPA AQS annual summaries on PlainAirData, Hawaii is #1 of 52 by day-weighted good-day share (93.8% of monitored days) at mean county median-AQI #4 (27.3) ≠ Alaska #1 lowest mean county median AQI (20.3) at good-day share #8 (84.4%). According to the 2025 EPA AQS county release on PlainAirData, Ponce County, Puerto Rico is #1 of 951 by median AQI (3, 91.4% Good days) at good-day-share #159 ≠ largest of 7 at 100.0% Good days #1 by good-day share (100.0%, median AQI 9) at median-AQI #7.

How every EPA-monitored day across the U.S. distributes on the AQI scale, the national baseline your county is measured against.
All U.S. monitored counties AQI category distribution Stacked-segment bar showing the share of monitored days that fell in each EPA AQI category, Good, Moderate, USG, Unhealthy, Very Unhealthy, Hazardous, with median AQI marker. AQI category distribution 323,288 monitored days G M Median AQI 38.5 0 50 100 150 200 300 500 All U.S. monitored counties
  • 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%

AQI Lookup

Search any U.S. county for its median AQI, EPA category, and good-day share.

County Compare

Put two or three counties side by side on the metrics that matter.

Cleanest Counties Finder

Rank the cleanest or most-polluted counties by state.

AQI Health Calculator

Enter an AQI value to see its category and EPA health guidance.

Cleanest county right now

Kenai Peninsula County, Alaska

100.0% good-air days, median AQI 9.

Most polluted county right now

Maricopa County, Arizona

8.8% good-air days, median AQI 73.

Frequently asked questions

What can the PlainAirData tools do?
The tools let you look up any county’s air quality, compare counties side by side, rank the cleanest or most-polluted counties by state, and translate any AQI value into plain-language health guidance. Each one runs on the same EPA Air Quality System data behind the rest of the site.
Is the data the same as the county pages?
Yes. Every tool queries the same EPA Air Quality System figures shown on the county, metro, and state profiles, so a value you find in a tool matches the full profile it links to. Nothing is estimated or fabricated.

Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files · 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.

Every figure on PlainAirData is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. Every tool on this hub reads from EPA AQS annual county monitoring summaries. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2025.