Indicators / United States / Air quality
Days when ozone 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
- 49.6% 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 | 49.6 |
| 2024 | 52.7 |
| 2023 | 45.5 |
| 2022 | 46.6 |
| 2021 | 43.1 |
| 2020 | 46.3 |
| 2019 | 51.5 |
| 2018 | 47.5 |
| 2017 | 50.4 |
| 2016 | 52.7 |
| 2015 | 48.8 |
| 2014 | 49.0 |
| 2013 | 49.7 |
| 2012 | 50.8 |
| 2011 | 48.5 |
| 2010 | 53.4 |
| 2009 | 53.6 |
| 2008 | 57.4 |
| 2007 | 56.9 |
| 2006 | 62.7 |
| 2005 | 63.3 |
| 2004 | 64.4 |
| 2003 | 67.2 |
| 2002 | 66.5 |
| 2001 | 68.0 |
| 2000 | 67.4 |
| 1999 | 71.9 |
| 1998 | 87.5 |
| 1997 | 85.4 |
| 1996 | 84.0 |
| 1995 | 84.4 |
| 1994 | 84.3 |
| 1993 | 81.4 |
| 1992 | 77.8 |
| 1991 | 79.8 |
| 1990 | 79.5 |
| 1989 | 68.5 |
| 1988 | 71.0 |
| 1987 | 69.3 |
| 1986 | 62.3 |
| 1985 | 63.1 |
| 1984 | 62.0 |
| 1983 | 60.8 |
| 1982 | 58.9 |
| 1981 | 60.6 |
| 1980 | 55.1 |
Highest and lowest counties, 2025
| Highest | State | Days when ozone set the AQI |
|---|---|---|
| Mayagüez Municipio | Puerto Rico | 100.0% of days |
| Walworth County | Wisconsin | 100.0% of days |
| Vilas County | Wisconsin | 100.0% of days |
| Taylor County | Wisconsin | 100.0% of days |
| Sheboygan County | Wisconsin | 100.0% of days |
| Rock County | Wisconsin | 100.0% of days |
| Racine County | Wisconsin | 100.0% of days |
| Manitowoc County | Wisconsin | 100.0% of days |
| La Crosse County | Wisconsin | 100.0% of days |
| Kewaunee County | Wisconsin | 100.0% of days |
| Lowest | State | Days when ozone set the AQI |
|---|---|---|
| Clay County | Alabama | 0.0% of days |
| Anchorage Municipality | Alaska | 0.0% of days |
| Juneau City and Borough | Alaska | 0.0% of days |
| Matanuska-Susitna Borough | Alaska | 0.0% of days |
| Mohave County | Arizona | 0.0% of days |
| Navajo County | Arizona | 0.0% of days |
| Santa Cruz County | Arizona | 0.0% of days |
| Del Norte County | California | 0.0% of days |
| Mono County | California | 0.0% of days |
| Plumas County | California | 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-ozone-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 ozone 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.