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)

Jefferson County had the highest share of days with good air quality (US EPA AQI) of 31 counties in 2023, at 96%. Okanogan County had the lowest, at 50.7%. The median was 86.2%. Source: EPA.

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Highest96Jefferson County
Lowest50.7Okanogan County
Median86.231 counties

Map of counties, 2023

Adams County: 90.4 %Asotin County: 51.3 %Benton County: 71.8 %Chelan County: 76.7 %Clallam County: 84.1 %Clark County: 77 %Columbia County: 87.4 %Cowlitz County: 88.5 %Franklin County: 87.9 %Garfield County: 93.2 %Grant County: 82.2 %Grays Harbor County: 92.9 %Jefferson County: 96 %King County: 58.6 %Kitsap County: 92.6 %Kittitas County: 78.6 %Klickitat County: 92.4 %Lewis County: 86.7 %Mason County: 86.2 %Okanogan County: 50.7 %Pacific County: 94.6 %Pierce County: 74.8 %Skagit County: 92.1 %Snohomish County: 67.4 %Spokane County: 70.4 %Stevens County: 55.9 %Thurston County: 91.3 %Walla Walla County: 82.2 %Whatcom County: 90.8 %Whitman County: 88.5 %Yakima County: 55.6 %
  • Under 67
  • 67 to 77
  • 77 to 86
  • 86 to 89
  • 89 to 92
  • 92 and over
  • No data
%, 2023. 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, 2023

Jefferson County: 96 %Jefferson County96Pacific County: 94.6 %Pacific County94.6Garfield County: 93.2 %Garfield County93.2Grays Harbor County: 92.9 %Grays Harbor County92.9Kitsap County: 92.6 %Kitsap County92.6Klickitat County: 92.4 %Klickitat County92.4Skagit County: 92.1 %Skagit County92.1Thurston County: 91.3 %Thurston County91.3Whatcom County: 90.8 %Whatcom County90.8Adams County: 90.4 %Adams County90.4Cowlitz County: 88.5 %Cowlitz County88.5Whitman County: 88.5 %Whitman County88.5Franklin County: 87.9 %Franklin County87.9Columbia County: 87.4 %Columbia County87.4Lewis County: 86.7 %Lewis County86.7Mason County: 86.2 %Mason County86.2Clallam County: 84.1 %Clallam County84.1Grant County: 82.2 %Grant County82.2Walla Walla County: 82.2 %Walla Walla County82.2Kittitas County: 78.6 %Kittitas County78.6Clark County: 77 %Clark County77Chelan County: 76.7 %Chelan County76.7Pierce County: 74.8 %Pierce County74.8Benton County: 71.8 %Benton County71.8Spokane County: 70.4 %Spokane County70.4Snohomish County: 67.4 %Snohomish County67.4King County: 58.6 %King County58.6Stevens County: 55.9 %Stevens County55.9Yakima County: 55.6 %Yakima County55.6Asotin County: 51.3 %Asotin County51.3Okanogan County: 50.7 %Okanogan County50.7Jefferson County: 96 %Jefferson County96Pacific County: 94.6 %Pacific County94.6Garfield County: 93.2 %Garfield County93.2Grays Harbor County: 92.9 %Grays Harbor County92.9Kitsap County: 92.6 %Kitsap County92.6Klickitat County: 92.4 %Klickitat County92.4Skagit County: 92.1 %Skagit County92.1Thurston County: 91.3 %Thurston County91.3Whatcom County: 90.8 %Whatcom County90.8Adams County: 90.4 %Adams County90.4Cowlitz County: 88.5 %Cowlitz County88.5Whitman County: 88.5 %Whitman County88.5Franklin County: 87.9 %Franklin County87.9Columbia County: 87.4 %Columbia County87.4Lewis County: 86.7 %Lewis County86.7Mason County: 86.2 %Mason County86.2Clallam County: 84.1 %Clallam County84.1Grant County: 82.2 %Grant County82.2Walla Walla County: 82.2 %Walla Walla County82.2Kittitas County: 78.6 %Kittitas County78.6Clark County: 77 %Clark County77Chelan County: 76.7 %Chelan County76.7Pierce County: 74.8 %Pierce County74.8Benton County: 71.8 %Benton County71.8Spokane County: 70.4 %Spokane County70.4Snohomish County: 67.4 %Snohomish County67.4King County: 58.6 %King County58.6Stevens County: 55.9 %Stevens County55.9Yakima County: 55.6 %Yakima County55.6Asotin County: 51.3 %Asotin County51.3Okanogan County: 50.7 %Okanogan County50.7
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2023 (%)Change on 2022
1Jefferson County96+2.3 pts
2Pacific County94.6n/a
3Garfield County93.2+5.8 pts
4Grays Harbor County92.9-0.3 pts
5Kitsap County92.6+7.4 pts
6Klickitat County92.4+4.4 pts
7Skagit County92.1+6.3 pts
8Thurston County91.3+2.5 pts
9Whatcom County90.8+5.1 pts
10Adams County90.4+0.8 pts
11Cowlitz County88.5+1.4 pts
11Whitman County88.5+4.7 pts
13Franklin County87.9+5.9 pts
14Columbia County87.4+1.4 pts
15Lewis County86.7+8.6 pts
16Mason County86.2+3.5 pts
17Clallam County84.1+9.6 pts
18Grant County82.2+5.8 pts
18Walla Walla County82.2+2.2 pts
20Kittitas County78.6+7.4 pts
21Clark County77+3.8 pts
22Chelan County76.7+9.3 pts
23Pierce County74.8+9.3 pts
24Benton County71.8-4.4 pts
25Spokane County70.4+0.8 pts
26Snohomish County67.4+9.4 pts
27King County58.6-0.6 pts
28Stevens County55.9-1.1 pts
29Yakima County55.6+6.8 pts
30Asotin County51.3-3.2 pts
31Okanogan County50.7+2.8 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 2023 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), 2023) [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), 2023. 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?period=2023. 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), 2023. 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?period=2023.

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), 2023 [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?period=2023 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_washington_by_2023,
  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), 2023}},
  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?period=2023. 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), 2023
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?period=2023
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2023.
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)?

Jefferson County, with 96% in 2023, according to EPA.

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

Okanogan County, with 50.7% in 2023.

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 2023 and are not ranked.

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

Counties in Washington: more rankings