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)

Pacific County had the highest share of days with good air quality (US EPA AQI) of 31 counties in 2024, at 99.7%. Okanogan County had the lowest, at 61.5%. The median was 87.7%. Source: EPA.

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Highest99.7Pacific County
Lowest61.5Okanogan County
Median87.731 counties

Map of counties, 2024

Adams County: 93.4 %Asotin County: 62 %Benton County: 81.7 %Chelan County: 80.1 %Clallam County: 87.7 %Clark County: 87.7 %Columbia County: 90.4 %Cowlitz County: 95.4 %Franklin County: 90.2 %Garfield County: 90.2 %Grant County: 86.9 %Grays Harbor County: 96.4 %Jefferson County: 96.5 %King County: 69.7 %Kitsap County: 97.2 %Kittitas County: 87.4 %Klickitat County: 95.3 %Lewis County: 93.3 %Mason County: 93.2 %Okanogan County: 61.5 %Pacific County: 99.7 %Pierce County: 72.4 %Skagit County: 97.5 %Snohomish County: 71.6 %Spokane County: 76.5 %Stevens County: 70.2 %Thurston County: 93.4 %Walla Walla County: 85.8 %Whatcom County: 92.8 %Whitman County: 84.7 %Yakima County: 67.8 %
  • Under 72
  • 72 to 85
  • 85 to 88
  • 88 to 93
  • 93 to 95
  • 95 and over
  • No data
%, 2024. 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, 2024

Pacific County: 99.7 %Pacific County99.7Skagit County: 97.5 %Skagit County97.5Kitsap County: 97.2 %Kitsap County97.2Jefferson County: 96.5 %Jefferson County96.5Grays Harbor County: 96.4 %Grays Harbor County96.4Cowlitz County: 95.4 %Cowlitz County95.4Klickitat County: 95.3 %Klickitat County95.3Adams County: 93.4 %Adams County93.4Thurston County: 93.4 %Thurston County93.4Lewis County: 93.3 %Lewis County93.3Mason County: 93.2 %Mason County93.2Whatcom County: 92.8 %Whatcom County92.8Columbia County: 90.4 %Columbia County90.4Franklin County: 90.2 %Franklin County90.2Garfield County: 90.2 %Garfield County90.2Clallam County: 87.7 %Clallam County87.7Clark County: 87.7 %Clark County87.7Kittitas County: 87.4 %Kittitas County87.4Grant County: 86.9 %Grant County86.9Walla Walla County: 85.8 %Walla Walla County85.8Whitman County: 84.7 %Whitman County84.7Benton County: 81.7 %Benton County81.7Chelan County: 80.1 %Chelan County80.1Spokane County: 76.5 %Spokane County76.5Pierce County: 72.4 %Pierce County72.4Snohomish County: 71.6 %Snohomish County71.6Stevens County: 70.2 %Stevens County70.2King County: 69.7 %King County69.7Yakima County: 67.8 %Yakima County67.8Asotin County: 62 %Asotin County62Okanogan County: 61.5 %Okanogan County61.5Pacific County: 99.7 %Pacific County99.7Skagit County: 97.5 %Skagit County97.5Kitsap County: 97.2 %Kitsap County97.2Jefferson County: 96.5 %Jefferson County96.5Grays Harbor County: 96.4 %Grays Harbor County96.4Cowlitz County: 95.4 %Cowlitz County95.4Klickitat County: 95.3 %Klickitat County95.3Adams County: 93.4 %Adams County93.4Thurston County: 93.4 %Thurston County93.4Lewis County: 93.3 %Lewis County93.3Mason County: 93.2 %Mason County93.2Whatcom County: 92.8 %Whatcom County92.8Columbia County: 90.4 %Columbia County90.4Franklin County: 90.2 %Franklin County90.2Garfield County: 90.2 %Garfield County90.2Clallam County: 87.7 %Clallam County87.7Clark County: 87.7 %Clark County87.7Kittitas County: 87.4 %Kittitas County87.4Grant County: 86.9 %Grant County86.9Walla Walla County: 85.8 %Walla Walla County85.8Whitman County: 84.7 %Whitman County84.7Benton County: 81.7 %Benton County81.7Chelan County: 80.1 %Chelan County80.1Spokane County: 76.5 %Spokane County76.5Pierce County: 72.4 %Pierce County72.4Snohomish County: 71.6 %Snohomish County71.6Stevens County: 70.2 %Stevens County70.2King County: 69.7 %King County69.7Yakima County: 67.8 %Yakima County67.8Asotin County: 62 %Asotin County62Okanogan County: 61.5 %Okanogan County61.5
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2024 (%)Change on 2023
1Pacific County99.7+5.1 pts
2Skagit County97.5+5.4 pts
3Kitsap County97.2+4.6 pts
4Jefferson County96.5+0.5 pts
5Grays Harbor County96.4+3.5 pts
6Cowlitz County95.4+6.9 pts
7Klickitat County95.3+2.9 pts
8Adams County93.4+3 pts
8Thurston County93.4+2.1 pts
10Lewis County93.3+6.6 pts
11Mason County93.2+7 pts
12Whatcom County92.8+2 pts
13Columbia County90.4+3 pts
14Franklin County90.2+2.3 pts
14Garfield County90.2-3 pts
16Clallam County87.7+3.6 pts
16Clark County87.7+10.7 pts
18Kittitas County87.4+8.8 pts
19Grant County86.9+4.7 pts
20Walla Walla County85.8+3.6 pts
21Whitman County84.7-3.8 pts
22Benton County81.7+9.9 pts
23Chelan County80.1+3.4 pts
24Spokane County76.5+6.1 pts
25Pierce County72.4-2.4 pts
26Snohomish County71.6+4.2 pts
27Stevens County70.2+14.3 pts
28King County69.7+11.1 pts
29Yakima County67.8+12.2 pts
30Asotin County62+10.7 pts
31Okanogan County61.5+10.8 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 2024 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), 2024) [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), 2024. 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=2024. 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), 2024. 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=2024.

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), 2024 [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=2024 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_washington_by_2024,
  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), 2024}},
  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=2024. 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), 2024
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=2024
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2024.
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 2024, according to EPA.

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

Okanogan County, with 61.5% in 2024.

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 2024 and are not ranked.

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

Counties in Washington: more rankings