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)

Klickitat County had the highest share of days with good air quality (US EPA AQI) of 29 counties in 2014, at 95.8%. King County had the lowest, at 51.5%. The median was 84.2%. Source: EPA.

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Highest95.8Klickitat County
Lowest51.5King County
Median84.229 counties

Map of counties, 2014

Adams County: 91.6 %Asotin County: 76.2 %Benton County: 84.8 %Chelan County: 64.6 %Clallam County: 76.4 %Clark County: 72.9 %Columbia County: 90.8 %Cowlitz County: 84.8 %Franklin County: 87.5 %Grant County: 83 %Grays Harbor County: 87.4 %Jefferson County: 88.3 %King County: 51.5 %Kitsap County: 92.8 %Kittitas County: 84.2 %Klickitat County: 95.8 %Lewis County: 85.5 %Mason County: 87.4 %Okanogan County: 55.3 %Pierce County: 68.8 %Skagit County: 87.4 %Snohomish County: 66 %Spokane County: 63 %Stevens County: 61.1 %Thurston County: 81 %Walla Walla County: 90.3 %Whatcom County: 69.6 %Whitman County: 88.2 %Yakima County: 62.2 %
  • Under 65
  • 65 to 77
  • 77 to 85
  • 85 to 88
  • 88 and over
  • No data
%, 2014. 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, 2014

Klickitat County: 95.8 %Klickitat County95.8Kitsap County: 92.8 %Kitsap County92.8Adams County: 91.6 %Adams County91.6Columbia County: 90.8 %Columbia County90.8Walla Walla County: 90.3 %Walla Walla County90.3Jefferson County: 88.3 %Jefferson County88.3Whitman County: 88.2 %Whitman County88.2Franklin County: 87.5 %Franklin County87.5Grays Harbor County: 87.4 %Grays Harbor County87.4Mason County: 87.4 %Mason County87.4Skagit County: 87.4 %Skagit County87.4Lewis County: 85.5 %Lewis County85.5Benton County: 84.8 %Benton County84.8Cowlitz County: 84.8 %Cowlitz County84.8Kittitas County: 84.2 %Kittitas County84.2Grant County: 83 %Grant County83Thurston County: 81 %Thurston County81Clallam County: 76.4 %Clallam County76.4Asotin County: 76.2 %Asotin County76.2Clark County: 72.9 %Clark County72.9Whatcom County: 69.6 %Whatcom County69.6Pierce County: 68.8 %Pierce County68.8Snohomish County: 66 %Snohomish County66Chelan County: 64.6 %Chelan County64.6Spokane County: 63 %Spokane County63Yakima County: 62.2 %Yakima County62.2Stevens County: 61.1 %Stevens County61.1Okanogan County: 55.3 %Okanogan County55.3King County: 51.5 %King County51.5Klickitat County: 95.8 %Klickitat County95.8Kitsap County: 92.8 %Kitsap County92.8Adams County: 91.6 %Adams County91.6Columbia County: 90.8 %Columbia County90.8Walla Walla County: 90.3 %Walla Walla County90.3Jefferson County: 88.3 %Jefferson County88.3Whitman County: 88.2 %Whitman County88.2Franklin County: 87.5 %Franklin County87.5Grays Harbor County: 87.4 %Grays Harbor County87.4Mason County: 87.4 %Mason County87.4Skagit County: 87.4 %Skagit County87.4Lewis County: 85.5 %Lewis County85.5Benton County: 84.8 %Benton County84.8Cowlitz County: 84.8 %Cowlitz County84.8Kittitas County: 84.2 %Kittitas County84.2Grant County: 83 %Grant County83Thurston County: 81 %Thurston County81Clallam County: 76.4 %Clallam County76.4Asotin County: 76.2 %Asotin County76.2Clark County: 72.9 %Clark County72.9Whatcom County: 69.6 %Whatcom County69.6Pierce County: 68.8 %Pierce County68.8Snohomish County: 66 %Snohomish County66Chelan County: 64.6 %Chelan County64.6Spokane County: 63 %Spokane County63Yakima County: 62.2 %Yakima County62.2Stevens County: 61.1 %Stevens County61.1Okanogan County: 55.3 %Okanogan County55.3King County: 51.5 %King County51.5
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2014 (%)Change on 2013
1Klickitat County95.8+4.3 pts
2Kitsap County92.8+3.7 pts
3Adams County91.6-2.8 pts
4Columbia County90.8+7.6 pts
5Walla Walla County90.3+11.7 pts
6Jefferson County88.3-0.1 pts
7Whitman County88.2+8.5 pts
8Franklin County87.5+9.7 pts
9Grays Harbor County87.4+11.8 pts
9Mason County87.4+18.1 pts
9Skagit County87.4+10.7 pts
12Lewis County85.5+12.5 pts
13Benton County84.8+7.7 pts
13Cowlitz County84.8+7.3 pts
15Kittitas County84.2+7.8 pts
16Grant County83+8.2 pts
17Thurston County81+10.7 pts
18Clallam County76.4-5 pts
19Asotin County76.2+13.7 pts
20Clark County72.9+7.7 pts
21Whatcom County69.6-9.1 pts
22Pierce County68.8+9.3 pts
23Snohomish County66+3.8 pts
24Chelan County64.6+1.6 pts
25Spokane County63+6 pts
26Yakima County62.2+14.5 pts
27Stevens County61.1+2.2 pts
28Okanogan County55.3+1.6 pts
29King County51.5+20.5 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. 5 counties with data in other periods have no value for 2014 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), 2014) [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), 2014. 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=2014. 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), 2014. 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=2014.

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), 2014 [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=2014 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_washington_by_2014,
  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), 2014}},
  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=2014. 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), 2014
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=2014
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2014.
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)?

Klickitat County, with 95.8% in 2014, according to EPA.

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

King County, with 51.5% in 2014.

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. 5 counties have no value for 2014 and are not ranked.

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

Counties in Washington: more rankings