# Counties in Washington by median 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_median`
- Unit: index
- Definition: Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries. The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide). Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: median 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: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/median-air-quality-index/washington-counties

| Rank | Place | index |
|---:|---|---:|
| 1 | Pierce County | 44 |
| 2 | King County | 43 |
| 2 | Spokane County | 43 |
| 4 | Asotin County | 42 |
| 5 | Okanogan County | 41 |
| 5 | Snohomish County | 41 |
| 5 | Yakima County | 41 |
| 8 | Benton County | 36 |
| 8 | Columbia County | 36 |
| 10 | Chelan County | 35 |
| 10 | Stevens County | 35 |
| 12 | Clark County | 33 |
| 13 | Whatcom County | 31 |
| 14 | Clallam County | 29 |
| 15 | Grant County | 28 |
| 15 | Walla Walla County | 28 |
| 17 | Thurston County | 27 |
| 18 | Kittitas County | 25 |
| 18 | Skagit County | 25 |
| 20 | Franklin County | 23 |
| 20 | Klickitat County | 23 |
| 20 | Mason County | 23 |
| 20 | Whitman County | 23 |
| 24 | Cowlitz County | 22 |
| 24 | Grays Harbor County | 22 |
| 24 | Kitsap County | 22 |
| 27 | Adams County | 21 |
| 28 | Jefferson County | 20 |
| 28 | Lewis County | 20 |
| 30 | Garfield County | 19 |
| 31 | Pacific County | 16 |