State air quality · 2025
Washington Air Quality Ranking
Across 31 monitored counties, the typical county in Washington posts a median AQI of 30 (Good) and 82.2% of monitored days were rated Good, from EPA AQS.
- 30
- Avg median AQI
- 82.2%
- Good-air days
- 31
- Counties monitored
- 75%
- Cleaner than US states
Washington's typical county median AQI is 30 (Good) across 31 monitored counties
According to the U.S. EPA Air Quality System, Washington monitors 31 counties with a day-weighted Good-day share of 82.2%. Cleanest: Pacific County (99.7% Good). Most polluted: Okanogan County (56.5%). These are annual summaries, not live AirNow readings.
Data source EPA Air Quality System (AQS)
- Cleaner than US states
- Washington's day-weighted Good-day share of 82.2% places it cleaner than 75% of US states.
- In-state spread
- Within Washington, Pacific County leads at 99.7% Good days while Okanogan County sits at 56.5% across 31 monitored counties.
- 2024→2025 release
- Washington's Good-day share moved -2.8 points vs the 2024 EPA annual release.
- Typical median AQI
- Typical median AQI: 30
Verify with AirNow → · EPA AQS →
EPA state monitoring brief
AQS state key WASHINGTON
Washington · 2025 EPA AQS · 31 counties · med AQI 30 · 82.2% Good · Pacific→Okanogan spread
- GOOD 30 Median AQI · Good
- SHARE 82.2% Good-day share
- COUNT 31 Counties monitored
- UNH 21 Unhealthy+ days
- RANK 75% Cleaner than states
- PM25 87.1% Main pollutant share
Good-day share peers
Washington's 82.2% Good-day share is cleaner than 75% of monitored US states; Pacific and Okanogan County bracket the in-state range. Open Pacific County →
According to EPA AQS annual summaries on PlainAirData, Washington ranks #13 of 52 by day-weighted good-day share (82.2%) and #5 by mean county median AQI (29.6). Hawaii is #1 of 52 by day-weighted good-day share (93.8% of monitored days) at mean county median-AQI #4 (27.3) ≠ Alaska #1 lowest mean county median AQI (20.3) at good-day share #8 (84.4%).
Data updated August 2026
What changed, what drives it, and how thick is the sample
Three derived views WPR-style word count does not substitute for: release-over-release movement from county annual rows, the EPA main-pollutant day mix, and how many counties sit below the 100-day ranking floor.
Release change
82.2%
Good-day share in 2025, down 2.8 percentage points vs 2024. County-mean median AQI 30, 1.6 points higher (worse) than 2024.
Pollutant mix
PM2.5
Main driver on 87.1% of pollutant-assigned days.
- PM2.5 87.1%
- Ozone 11.0%
- PM10 1.8%
- NO2 0.1%
Monitoring coverage
346
Average monitored days per county in the latest release. 1 of 31 counties sit below the 100-day floor used for cleanest/most-polluted claims.
Counties Monitored
31
Good Days %
82.2%
Avg Median AQI
30
Total Unhealthy Days
21
Best Air Quality
Pacific County
Worst Air Quality
Okanogan County
Where Washington sits nationally
COUNT-derived placement among 52 US states with at least 365 monitored days in the latest county release. Washington's day-weighted Good-day share is 82.2% - cleaner than 75% of that comparison set.
Washington Good-day share vs. every US state
Day-weighted share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
82.2% Cleaner than 75% higher than 75% of 52 US states
Each bar is a band; taller bars hold more US states. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.
Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025
Which counties in Washington have the cleanest and most polluted air?
Cleanest counties in Washington
| County | Good % | Median AQI | Max AQI | Unhealthy Days |
|---|---|---|---|---|
| Pacific | 99.7% | 16 | 51 | 0 |
| Skagit | 97.5% | 25 | 57 | 0 |
| Jefferson | 97.3% | 20 | 59 | 0 |
| Grays Harbor | 97.3% | 22 | 76 | 0 |
| Kitsap | 95.5% | 22 | 61 | 0 |
| Whatcom | 94.0% | 31 | 152 | 1 |
| Thurston | 93.5% | 27 | 65 | 0 |
| Garfield | 92.5% | 19 | 97 | 0 |
| Lewis | 91.3% | 20 | 74 | 0 |
| Adams | 90.5% | 21 | 99 | 0 |
| Columbia | 90.4% | 36 | 94 | 0 |
| Mason | 90.4% | 23 | 159 | 1 |
| Cowlitz | 90.4% | 22 | 72 | 0 |
| Whitman | 86.8% | 23 | 99 | 0 |
| Franklin | 86.7% | 23 | 109 | 0 |
| Clallam | 85.5% | 29 | 69 | 0 |
| Klickitat | 84.6% | 23 | 119 | 0 |
| Clark | 82.7% | 33 | 83 | 0 |
| Walla Walla | 80.8% | 28 | 85 | 0 |
| Benton | 80.3% | 36 | 113 | 0 |
| Kittitas | 80.0% | 25 | 114 | 0 |
| Grant | 79.7% | 28 | 154 | 1 |
| Pierce | 73.2% | 44 | 100 | 0 |
| Chelan | 69.6% | 35 | 233 | 9 |
| Stevens | 69.0% | 35 | 243 | 6 |
| Snohomish | 68.0% | 41 | 125 | 0 |
| King | 67.1% | 43 | 97 | 0 |
| Spokane | 64.7% | 43 | 126 | 0 |
| Yakima | 61.9% | 41 | 154 | 1 |
| Asotin | 61.9% | 42 | 151 | 1 |
| Okanogan | 56.5% | 41 | 160 | 1 |
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025. See our methodology for how AQI and median figures are computed.
Coverage: 31 counties in Washington with active monitoring stations. Unmonitored counties are not represented.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files, aggregated to the state level · 2020–2025
Every figure on PlainAirData is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.