# Counties in Washington by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2025

All 31 values come from U.S. Environmental Protection Agency for 2025, so the places are comparable. 3 counties have no value for that period and are not ranked.

- Indicator id: `aqi_unhealthy_sensitive_or_worse_days_share`
- Unit: %
- Definition: Days with a daily Air Quality Index above 100 (unhealthy for sensitive groups, unhealthy, very unhealthy or hazardous) as a percentage of the days of the year with an AQI in a US county. Calculated by Invokely from the day counts in the EPA AirData annual summaries; the counts are stored with each value.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts (https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual)
- Retrieved: 2026-10-12
- Citation: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/unhealthy-air-quality-days-share/washington-counties

| Rank | Place | % |
|---:|---|---:|
| 1 | Chelan County | 3.8 |
| 2 | Stevens County | 2.5 |
| 3 | Klickitat County | 1.1 |
| 3 | Okanogan County | 1.1 |
| 5 | Asotin County | 0.8 |
| 5 | Grant County | 0.8 |
| 5 | Kittitas County | 0.8 |
| 5 | Spokane County | 0.8 |
| 5 | Yakima County | 0.8 |
| 10 | Franklin County | 0.6 |
| 11 | Benton County | 0.5 |
| 12 | Mason County | 0.3 |
| 12 | Snohomish County | 0.3 |
| 12 | Whatcom County | 0.3 |
| 15 | Adams County | 0 |
| 15 | Clallam County | 0 |
| 15 | Clark County | 0 |
| 15 | Columbia County | 0 |
| 15 | Cowlitz County | 0 |
| 15 | Garfield County | 0 |
| 15 | Grays Harbor County | 0 |
| 15 | Jefferson County | 0 |
| 15 | King County | 0 |
| 15 | Kitsap County | 0 |
| 15 | Lewis County | 0 |
| 15 | Pacific County | 0 |
| 15 | Pierce County | 0 |
| 15 | Skagit County | 0 |
| 15 | Thurston County | 0 |
| 15 | Walla Walla County | 0 |
| 15 | Whitman County | 0 |