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)

San Juan County had the highest share of days with good air quality (US EPA AQI) of 31 counties in 2019, at 99.1%. Yakima County had the lowest, at 48.8%. The median was 82.2%. Source: EPA.

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Highest99.1San Juan County
Lowest48.8Yakima County
Median82.231 counties

Map of counties, 2019

Adams County: 94.2 %Asotin County: 70 %Benton County: 75 %Chelan County: 70.7 %Clallam County: 78.1 %Clark County: 76.1 %Columbia County: 88.2 %Cowlitz County: 83.6 %Franklin County: 86.5 %Garfield County: 92.2 %Grant County: 83.8 %Grays Harbor County: 92.9 %Jefferson County: 94.2 %King County: 57 %Kitsap County: 92.1 %Kittitas County: 73.4 %Klickitat County: 82.2 %Lewis County: 84.4 %Mason County: 84.5 %Okanogan County: 57.3 %Pierce County: 64.1 %San Juan County: 99.1 %Skagit County: 93.2 %Snohomish County: 62.4 %Spokane County: 70.7 %Stevens County: 61.1 %Thurston County: 79.5 %Walla Walla County: 81.9 %Whatcom County: 92 %Whitman County: 88.8 %Yakima County: 48.8 %
  • Under 64
  • 64 to 75
  • 75 to 82
  • 82 to 87
  • 87 to 92
  • 92 and over
  • No data
%, 2019. 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, 2019

San Juan County: 99.1 %San Juan County99.1Adams County: 94.2 %Adams County94.2Jefferson County: 94.2 %Jefferson County94.2Skagit County: 93.2 %Skagit County93.2Grays Harbor County: 92.9 %Grays Harbor County92.9Garfield County: 92.2 %Garfield County92.2Kitsap County: 92.1 %Kitsap County92.1Whatcom County: 92 %Whatcom County92Whitman County: 88.8 %Whitman County88.8Columbia County: 88.2 %Columbia County88.2Franklin County: 86.5 %Franklin County86.5Mason County: 84.5 %Mason County84.5Lewis County: 84.4 %Lewis County84.4Grant County: 83.8 %Grant County83.8Cowlitz County: 83.6 %Cowlitz County83.6Klickitat County: 82.2 %Klickitat County82.2Walla Walla County: 81.9 %Walla Walla County81.9Thurston County: 79.5 %Thurston County79.5Clallam County: 78.1 %Clallam County78.1Clark County: 76.1 %Clark County76.1Benton County: 75 %Benton County75Kittitas County: 73.4 %Kittitas County73.4Chelan County: 70.7 %Chelan County70.7Spokane County: 70.7 %Spokane County70.7Asotin County: 70 %Asotin County70Pierce County: 64.1 %Pierce County64.1Snohomish County: 62.4 %Snohomish County62.4Stevens County: 61.1 %Stevens County61.1Okanogan County: 57.3 %Okanogan County57.3King County: 57 %King County57Yakima County: 48.8 %Yakima County48.8San Juan County: 99.1 %San Juan County99.1Adams County: 94.2 %Adams County94.2Jefferson County: 94.2 %Jefferson County94.2Skagit County: 93.2 %Skagit County93.2Grays Harbor County: 92.9 %Grays Harbor County92.9Garfield County: 92.2 %Garfield County92.2Kitsap County: 92.1 %Kitsap County92.1Whatcom County: 92 %Whatcom County92Whitman County: 88.8 %Whitman County88.8Columbia County: 88.2 %Columbia County88.2Franklin County: 86.5 %Franklin County86.5Mason County: 84.5 %Mason County84.5Lewis County: 84.4 %Lewis County84.4Grant County: 83.8 %Grant County83.8Cowlitz County: 83.6 %Cowlitz County83.6Klickitat County: 82.2 %Klickitat County82.2Walla Walla County: 81.9 %Walla Walla County81.9Thurston County: 79.5 %Thurston County79.5Clallam County: 78.1 %Clallam County78.1Clark County: 76.1 %Clark County76.1Benton County: 75 %Benton County75Kittitas County: 73.4 %Kittitas County73.4Chelan County: 70.7 %Chelan County70.7Spokane County: 70.7 %Spokane County70.7Asotin County: 70 %Asotin County70Pierce County: 64.1 %Pierce County64.1Snohomish County: 62.4 %Snohomish County62.4Stevens County: 61.1 %Stevens County61.1Okanogan County: 57.3 %Okanogan County57.3King County: 57 %King County57Yakima County: 48.8 %Yakima County48.8
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2019 (%)Change on 2018
1San Juan County99.1n/a
2Adams County94.2+9.9 pts
2Jefferson County94.2+3.1 pts
4Skagit County93.2+4.2 pts
5Grays Harbor County92.9+4.1 pts
6Garfield County92.2+7 pts
7Kitsap County92.1+0.7 pts
8Whatcom County92+3.6 pts
9Whitman County88.8+5.8 pts
10Columbia County88.2+6.8 pts
11Franklin County86.5+3.2 pts
12Mason County84.5+1.2 pts
13Lewis County84.4+2.8 pts
14Grant County83.8+4.6 pts
15Cowlitz County83.6-1.3 pts
16Klickitat County82.2+4.8 pts
17Walla Walla County81.9+1.9 pts
18Thurston County79.5-5.3 pts
19Clallam County78.1+11.5 pts
20Clark County76.1+1.6 pts
21Benton County75-0.3 pts
22Kittitas County73.4-7.6 pts
23Chelan County70.7+3.9 pts
23Spokane County70.7+5.5 pts
25Asotin County70+4.2 pts
26Pierce County64.10 pts
27Snohomish County62.4-8.8 pts
28Stevens County61.1+6.3 pts
29Okanogan County57.3+9.6 pts
30King County57-1.1 pts
31Yakima County48.8+1.4 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 2019 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), 2019) [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), 2019. 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=2019. 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), 2019. 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=2019.

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), 2019 [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=2019 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_washington_by_2019,
  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), 2019}},
  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=2019. 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), 2019
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=2019
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2019.
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)?

San Juan County, with 99.1% in 2019, according to EPA.

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

Yakima County, with 48.8% in 2019.

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 2019 and are not ranked.

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

Counties in Washington: more rankings