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 2021, at 98.3%. Okanogan County had the lowest, at 40%. The median was 84.7%. Source: EPA.

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Highest98.3Jefferson County
Lowest40Okanogan County
Median84.731 counties

Map of counties, 2021

Adams County: 91.5 %Asotin County: 52.5 %Benton County: 77.5 %Chelan County: 76.4 %Clallam County: 81.6 %Clark County: 84.4 %Columbia County: 83.3 %Cowlitz County: 97.3 %Franklin County: 92.8 %Garfield County: 85 %Grant County: 84.9 %Grays Harbor County: 95.1 %Jefferson County: 98.3 %King County: 67.9 %Kitsap County: 95.3 %Kittitas County: 83 %Klickitat County: 86.6 %Lewis County: 93.7 %Mason County: 93.9 %Okanogan County: 40 %Pend Oreille County: 70.8 %Pierce County: 73.7 %Skagit County: 94.3 %Snohomish County: 67.9 %Spokane County: 66.3 %Stevens County: 55.6 %Thurston County: 93.9 %Walla Walla County: 84.7 %Whatcom County: 97.3 %Whitman County: 84.9 %Yakima County: 47.9 %
  • Under 68
  • 68 to 78
  • 78 to 85
  • 85 to 92
  • 92 to 94
  • 94 and over
  • No data
%, 2021. 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, 2021

Jefferson County: 98.3 %Jefferson County98.3Cowlitz County: 97.3 %Cowlitz County97.3Whatcom County: 97.3 %Whatcom County97.3Kitsap County: 95.3 %Kitsap County95.3Grays Harbor County: 95.1 %Grays Harbor County95.1Skagit County: 94.3 %Skagit County94.3Mason County: 93.9 %Mason County93.9Thurston County: 93.9 %Thurston County93.9Lewis County: 93.7 %Lewis County93.7Franklin County: 92.8 %Franklin County92.8Adams County: 91.5 %Adams County91.5Klickitat County: 86.6 %Klickitat County86.6Garfield County: 85 %Garfield County85Grant County: 84.9 %Grant County84.9Whitman County: 84.9 %Whitman County84.9Walla Walla County: 84.7 %Walla Walla County84.7Clark County: 84.4 %Clark County84.4Columbia County: 83.3 %Columbia County83.3Kittitas County: 83 %Kittitas County83Clallam County: 81.6 %Clallam County81.6Benton County: 77.5 %Benton County77.5Chelan County: 76.4 %Chelan County76.4Pierce County: 73.7 %Pierce County73.7Pend Oreille County: 70.8 %Pend Oreille County70.8King County: 67.9 %King County67.9Snohomish County: 67.9 %Snohomish County67.9Spokane County: 66.3 %Spokane County66.3Stevens County: 55.6 %Stevens County55.6Asotin County: 52.5 %Asotin County52.5Yakima County: 47.9 %Yakima County47.9Okanogan County: 40 %Okanogan County40Jefferson County: 98.3 %Jefferson County98.3Cowlitz County: 97.3 %Cowlitz County97.3Whatcom County: 97.3 %Whatcom County97.3Kitsap County: 95.3 %Kitsap County95.3Grays Harbor County: 95.1 %Grays Harbor County95.1Skagit County: 94.3 %Skagit County94.3Mason County: 93.9 %Mason County93.9Thurston County: 93.9 %Thurston County93.9Lewis County: 93.7 %Lewis County93.7Franklin County: 92.8 %Franklin County92.8Adams County: 91.5 %Adams County91.5Klickitat County: 86.6 %Klickitat County86.6Garfield County: 85 %Garfield County85Grant County: 84.9 %Grant County84.9Whitman County: 84.9 %Whitman County84.9Walla Walla County: 84.7 %Walla Walla County84.7Clark County: 84.4 %Clark County84.4Columbia County: 83.3 %Columbia County83.3Kittitas County: 83 %Kittitas County83Clallam County: 81.6 %Clallam County81.6Benton County: 77.5 %Benton County77.5Chelan County: 76.4 %Chelan County76.4Pierce County: 73.7 %Pierce County73.7Pend Oreille County: 70.8 %Pend Oreille County70.8King County: 67.9 %King County67.9Snohomish County: 67.9 %Snohomish County67.9Spokane County: 66.3 %Spokane County66.3Stevens County: 55.6 %Stevens County55.6Asotin County: 52.5 %Asotin County52.5Yakima County: 47.9 %Yakima County47.9Okanogan County: 40 %Okanogan County40
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2021 (%)Change on 2020
1Jefferson County98.3+3.9 pts
2Cowlitz County97.3+6.9 pts
2Whatcom County97.3+4.1 pts
4Kitsap County95.3+6.1 pts
5Grays Harbor County95.1+4.9 pts
6Skagit County94.3-3.5 pts
7Mason County93.9+6.5 pts
7Thurston County93.9+7.6 pts
9Lewis County93.70 pts
10Franklin County92.8-0.4 pts
11Adams County91.5-3.3 pts
12Klickitat County86.6-2.7 pts
13Garfield County85-6 pts
14Grant County84.9-3.9 pts
14Whitman County84.9-6.6 pts
16Walla Walla County84.7+3.6 pts
17Clark County84.4+10.1 pts
18Columbia County83.3-5.2 pts
19Kittitas County83+1.6 pts
20Clallam County81.6-1.5 pts
21Benton County77.5-0.3 pts
22Chelan County76.4+1.5 pts
23Pierce County73.7+3.8 pts
24Pend Oreille County70.8+15.8 pts
25King County67.9+0.1 pts
25Snohomish County67.9+4 pts
27Spokane County66.3-11.8 pts
28Stevens County55.6-4.2 pts
29Asotin County52.5-12.9 pts
30Yakima County47.9-6.2 pts
31Okanogan County40-13.6 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 2021 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), 2021) [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), 2021. 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=2021. 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), 2021. 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=2021.

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), 2021 [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=2021 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_washington_by_2021,
  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), 2021}},
  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=2021. 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), 2021
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=2021
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2021.
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 98.3% in 2021, according to EPA.

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

Okanogan County, with 40% in 2021.

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 2021 and are not ranked.

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

Counties in Washington: more rankings