Data / Rankings / Share of days with good air quality (US EPA AQI) / Counties in Washington

Counties in Washington by share of days with good air quality (US EPA AQI), 2025

Pacific County had the highest share of days with good air quality (US EPA AQI) of 31 counties in 2025, at 99.7%. Okanogan County had the lowest, at 56.5%. The median was 85.5%. Source: EPA.

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Highest99.7Pacific County
Lowest56.5Okanogan County
Median85.531 counties

Map of counties, 2025

Adams County: 90.5 %Asotin County: 61.9 %Benton County: 80.3 %Chelan County: 69.6 %Clallam County: 85.5 %Clark County: 82.7 %Columbia County: 90.4 %Cowlitz County: 90.4 %Franklin County: 86.7 %Garfield County: 92.5 %Grant County: 79.7 %Grays Harbor County: 97.3 %Jefferson County: 97.3 %King County: 67.1 %Kitsap County: 95.5 %Kittitas County: 80 %Klickitat County: 84.6 %Lewis County: 91.3 %Mason County: 90.4 %Okanogan County: 56.5 %Pacific County: 99.7 %Pierce County: 73.2 %Skagit County: 97.5 %Snohomish County: 67.9 %Spokane County: 64.7 %Stevens County: 69 %Thurston County: 93.5 %Walla Walla County: 80.8 %Whatcom County: 94 %Whitman County: 86.8 %Yakima County: 61.9 %
  • Under 68
  • 68 to 80
  • 80 to 86
  • 86 to 90
  • 90 to 94
  • 94 and over
  • No data
%, 2025. Hatched areas have no value for this period. Source: Invokely calculation with data from EPA. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2025

Pacific County: 99.7 %Pacific County99.7Skagit County: 97.5 %Skagit County97.5Grays Harbor County: 97.3 %Grays Harbor County97.3Jefferson County: 97.3 %Jefferson County97.3Kitsap County: 95.5 %Kitsap County95.5Whatcom County: 94 %Whatcom County94Thurston County: 93.5 %Thurston County93.5Garfield County: 92.5 %Garfield County92.5Lewis County: 91.3 %Lewis County91.3Adams County: 90.5 %Adams County90.5Columbia County: 90.4 %Columbia County90.4Cowlitz County: 90.4 %Cowlitz County90.4Mason County: 90.4 %Mason County90.4Whitman County: 86.8 %Whitman County86.8Franklin County: 86.7 %Franklin County86.7Clallam County: 85.5 %Clallam County85.5Klickitat County: 84.6 %Klickitat County84.6Clark County: 82.7 %Clark County82.7Walla Walla County: 80.8 %Walla Walla County80.8Benton County: 80.3 %Benton County80.3Kittitas County: 80 %Kittitas County80Grant County: 79.7 %Grant County79.7Pierce County: 73.2 %Pierce County73.2Chelan County: 69.6 %Chelan County69.6Stevens County: 69 %Stevens County69Snohomish County: 67.9 %Snohomish County67.9King County: 67.1 %King County67.1Spokane County: 64.7 %Spokane County64.7Asotin County: 61.9 %Asotin County61.9Yakima County: 61.9 %Yakima County61.9Okanogan County: 56.5 %Okanogan County56.5Pacific County: 99.7 %Pacific County99.7Skagit County: 97.5 %Skagit County97.5Grays Harbor County: 97.3 %Grays Harbor County97.3Jefferson County: 97.3 %Jefferson County97.3Kitsap County: 95.5 %Kitsap County95.5Whatcom County: 94 %Whatcom County94Thurston County: 93.5 %Thurston County93.5Garfield County: 92.5 %Garfield County92.5Lewis County: 91.3 %Lewis County91.3Adams County: 90.5 %Adams County90.5Columbia County: 90.4 %Columbia County90.4Cowlitz County: 90.4 %Cowlitz County90.4Mason County: 90.4 %Mason County90.4Whitman County: 86.8 %Whitman County86.8Franklin County: 86.7 %Franklin County86.7Clallam County: 85.5 %Clallam County85.5Klickitat County: 84.6 %Klickitat County84.6Clark County: 82.7 %Clark County82.7Walla Walla County: 80.8 %Walla Walla County80.8Benton County: 80.3 %Benton County80.3Kittitas County: 80 %Kittitas County80Grant County: 79.7 %Grant County79.7Pierce County: 73.2 %Pierce County73.2Chelan County: 69.6 %Chelan County69.6Stevens County: 69 %Stevens County69Snohomish County: 67.9 %Snohomish County67.9King County: 67.1 %King County67.1Spokane County: 64.7 %Spokane County64.7Asotin County: 61.9 %Asotin County61.9Yakima County: 61.9 %Yakima County61.9Okanogan County: 56.5 %Okanogan County56.5
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2025 (%)Change on 2024
1Pacific County99.70 pts
2Skagit County97.50 pts
3Grays Harbor County97.3+0.9 pts
3Jefferson County97.3+0.8 pts
5Kitsap County95.5-1.7 pts
6Whatcom County94+1.2 pts
7Thurston County93.5+0.1 pts
8Garfield County92.5+2.3 pts
9Lewis County91.3-2 pts
10Adams County90.5-2.9 pts
11Columbia County90.40 pts
11Cowlitz County90.4-5 pts
11Mason County90.4-2.8 pts
14Whitman County86.8+2.1 pts
15Franklin County86.7-3.5 pts
16Clallam County85.5-2.2 pts
17Klickitat County84.6-10.7 pts
18Clark County82.7-5 pts
19Walla Walla County80.8-5 pts
20Benton County80.3-1.4 pts
21Kittitas County80-7.4 pts
22Grant County79.7-7.2 pts
23Pierce County73.2+0.8 pts
24Chelan County69.6-10.5 pts
25Stevens County69-1.2 pts
26Snohomish County67.9-3.7 pts
27King County67.1-2.6 pts
28Spokane County64.7-11.8 pts
29Asotin County61.9-0.1 pts
29Yakima County61.9-5.9 pts
31Okanogan County56.5-5 pts

Other periods

About this ranking

Days with a daily Air Quality Index of 0 to 50 (good) 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; both counts are stored with each value.

United States counties with air quality monitors only, about 1,000 of some 3,100 in recent years; a county without monitors has no value. The number of days with an AQI differs between counties because some monitors run only in the ozone season.

Every value in the ranking comes from the same publisher and the same period, so the counties are compared on one definition. 3 counties with data in other periods have no value for 2025 and are left out rather than filled from another source. Equal values share a rank.

How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days 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 styles

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

APA 7

U.S. Environmental Protection Agency. (2026). EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts (Counties in Washington by share of days with good air quality (US EPA AQI), 2025) [Data set]. Retrieved October 12, 2026, from https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual

MLA 9

EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts, Counties in Washington by share of days with good air quality (US EPA AQI), 2025. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. Counties in Washington by share of days with good air quality (US EPA AQI), 2025. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts, Counties in Washington by share of days with good air quality (US EPA AQI), 2025 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/good-air-quality-days-share/washington-counties (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_washington_by_2025,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts: Counties in Washington by share of days with good air quality (US EPA AQI), 2025}},
  year = {2026},
  howpublished = {Data set},
  url = {https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days 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.},
}
RIS
TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts: Counties in Washington by share of days with good air quality (US EPA AQI), 2025
PY  - 2026
DA  - 2026/07/13
PB  - U.S. Environmental Protection Agency
DB  - Invokely
UR  - https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual
L2  - https://invokely.ai/rankings/good-air-quality-days-share/washington-counties
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days 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.
ER  -
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Questions

Which county has the highest share of days with good air quality (US EPA AQI)?

Pacific County, with 99.7% in 2025, according to EPA.

Which county has the lowest share of days with good air quality (US EPA AQI)?

Okanogan County, with 56.5% in 2025.

Where does this ranking come from?

Every value comes from one source and one period, so the places are comparable: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 3 counties have no value for 2025 and are not ranked.

Share of days with good air quality (US EPA AQI): other rankings

Counties in Washington: more rankings