Indicators / United States / Air quality
Days when fine particles set the AQI
% of days · U.S. Environmental Protection Agency, AirData annual AQI by county, via airdata.dev · the pollutant with the highest AQI that day
- Middle county, 2025
- 46.0% of days
- States with a figure
- none county figures only
- Counties with a figure
- 916 2025
Show the numbers (46 rows)
| Year | Middle county |
|---|---|
| 2025 | 46.0 |
| 2024 | 43.4 |
| 2023 | 50.4 |
| 2022 | 47.7 |
| 2021 | 51.2 |
| 2020 | 49.2 |
| 2019 | 44.1 |
| 2018 | 47.3 |
| 2017 | 43.3 |
| 2016 | 37.6 |
| 2015 | 42.5 |
| 2014 | 38.5 |
| 2013 | 38.4 |
| 2012 | 35.9 |
| 2011 | 37.4 |
| 2010 | 33.3 |
| 2009 | 33.8 |
| 2008 | 28.4 |
| 2007 | 26.6 |
| 2006 | 24.5 |
| 2005 | 24.4 |
| 2004 | 23.2 |
| 2003 | 21.1 |
| 2002 | 21.9 |
| 2001 | 20.9 |
| 2000 | 20.5 |
| 1999 | 11.5 |
| 1998 | 0.0 |
| 1997 | 0.0 |
| 1996 | 0.0 |
| 1995 | 0.0 |
| 1994 | 0.0 |
| 1993 | 0.0 |
| 1992 | 0.0 |
| 1991 | 0.0 |
| 1990 | 0.0 |
| 1989 | 0.0 |
| 1988 | 0.0 |
| 1987 | 0.0 |
| 1986 | 0.0 |
| 1985 | 0.0 |
| 1984 | 0.0 |
| 1983 | 0.0 |
| 1982 | 0.0 |
| 1981 | 0.0 |
| 1980 | 0.0 |
Highest and lowest counties, 2025
| Highest | State | Days when fine particles set the AQI |
|---|---|---|
| Washakie County | Wyoming | 100.0% of days |
| Park County | Wyoming | 100.0% of days |
| Monroe County | Wisconsin | 100.0% of days |
| Jackson County | Wisconsin | 100.0% of days |
| Grant County | Wisconsin | 100.0% of days |
| Marshall County | West Virginia | 100.0% of days |
| Brooke County | West Virginia | 100.0% of days |
| Whitman County | Washington | 100.0% of days |
| Snohomish County | Washington | 100.0% of days |
| Pacific County | Washington | 100.0% of days |
| Lowest | State | Days when fine particles set the AQI |
|---|---|---|
| Elmore County | Alabama | 0.0% of days |
| Shelby County | Alabama | 0.0% of days |
| Clark County | Arkansas | 0.0% of days |
| Amador County | California | 0.0% of days |
| El Dorado County | California | 0.0% of days |
| Solano County | California | 0.0% of days |
| Sonoma County | California | 0.0% of days |
| Tuolumne County | California | 0.0% of days |
| Clear Creek County | Colorado | 0.0% of days |
| Gilpin County | Colorado | 0.0% of days |
Every county's figure is on its own page, in its profile table, with its rank among all counties and within its state.
Get this data
This page's numbers, as JSON:
curl https://visualizedata.org/data/us-indicators/us-pm25-days.jsonEvery place from airdata.dev (live, no key; U.S. Environmental Protection Agency data, this exact version):
curl "https://api.airdata.dev/v1/county-aqi-annual@2026-10-26.271cefd8c0/download/county-aqi-annual.parquet"Source
- U.S. Environmental Protection Agency, AirData annual AQI by county (U.S. public domain): EPA days PM2.5 was the main pollutant / days with an AQI.
- Read through airdata.dev, dataset county-aqi-annual, version 2026-10-26.271cefd8c0; its 47 input files from the U.S. Environmental Protection Agency are named with their sha256 in this page's data, and the site's checks recompute every figure from them.
- A year counts once it is over, for counties whose monitors gave an AQI on at least 180 days; EPA's file for the current year is partial. A county without a monitor has no figure, and one monitor can stand for a large county. Fine-particle (PM2.5) monitors only spread from 1999, and EPA has since tightened the AQI scale for ozone and fine particles, so a long trend mixes changes in the air with changes in what is measured and how.
- EPA refreshes its annual files twice a year; a year is final about May of the next.
- 12 areas in the source are not places in the geo registry and are left out: us-county-02261, us-county-09001, us-county-09003, us-county-09005, us-county-09007, us-county-09009, us-county-09011, us-county-09013, us-county-09015, us-county-78010, us-county-78020, us-county-78030 (Connecticut's former counties, retired Alaska and South Dakota codes, the Virgin Islands).
- Built 2026-10-27.