# Counties in Washington by highest daily Air Quality Index (US EPA), 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_max`
- Unit: index
- Definition: Highest daily Air Quality Index (AQI) value recorded in a US county during the year, from the EPA AirData annual summaries. Values above 500 are beyond the AQI scale and are published as EPA computes them.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: highest daily AQI (https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual)
- Publisher page: https://invokely.ai/en/publishers/environmental-protection-agency
- Retrieved: 2026-10-12
- Citation: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/highest-daily-air-quality-index/washington-counties

| Rank | Place | index |
|---:|---|---:|
| 1 | Stevens County | 243 |
| 2 | Chelan County | 233 |
| 3 | Okanogan County | 160 |
| 4 | Mason County | 159 |
| 5 | Grant County | 154 |
| 5 | Yakima County | 154 |
| 7 | Whatcom County | 152 |
| 8 | Asotin County | 151 |
| 9 | Spokane County | 126 |
| 10 | Snohomish County | 125 |
| 11 | Klickitat County | 119 |
| 12 | Kittitas County | 114 |
| 13 | Benton County | 113 |
| 14 | Franklin County | 109 |
| 15 | Pierce County | 100 |
| 16 | Adams County | 99 |
| 16 | Whitman County | 99 |
| 18 | Garfield County | 97 |
| 18 | King County | 97 |
| 20 | Columbia County | 94 |
| 21 | Walla Walla County | 85 |
| 22 | Clark County | 83 |
| 23 | Grays Harbor County | 76 |
| 24 | Lewis County | 74 |
| 25 | Cowlitz County | 72 |
| 26 | Clallam County | 69 |
| 27 | Thurston County | 65 |
| 28 | Kitsap County | 61 |
| 29 | Jefferson County | 59 |
| 30 | Skagit County | 57 |
| 31 | Pacific County | 51 |