Air quality tool

County Air Quality Compare

Put two or three counties side by side on the metrics that matter, with the best value in each row highlighted.

According to the U.S. Environmental Protection Agency (EPA), 977 monitored counties and 496 metro areas reported Air Quality Index readings through the federal Air Quality System (AQS) for the 2025 reporting year. This tool reads those official records directly; see the methodology for how every figure is computed.

More ways to explore

AQI lookupSearch a single county’s air quality. Cleanest counties finderRank the cleanest counties by state. AQI health calculatorWhat an AQI value means for health. Worst-air rankingsThe most polluted counties nationwide. Metro areasCompare metropolitan air quality. MethodologyHow the metrics are built.

Frequently asked questions

How does the county comparison work?
Enter two or three county names and the tool builds a side-by-side table of their median AQI, good-day share, moderate and unhealthy day counts, worst single-day reading, and how many days each was monitored, all from EPA Air Quality System data. The best value in each row is highlighted.
Why compare by good-day share instead of raw counts?
Counties are monitored for different numbers of days each year, so a raw count of clean days favors the most heavily monitored places. Good-day share is the percentage of monitored days rated Good, which lets a small county and a large metro compare on equal footing.
What if a county name matches more than one place?
The tool picks the best-matching monitored county for each name you enter and links it to its full profile so you can confirm it is the one you meant. Add the state name (for example, “Portland, Oregon”) to disambiguate common county or place names.

Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.