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)

Skagit County had the highest share of days with good air quality (US EPA AQI) of 31 counties in 2020, at 97.8%. Okanogan County had the lowest, at 53.6%. The median was 86.3%. Source: EPA.

Keep it in a collection in your library.
Highest97.8Skagit County
Lowest53.6Okanogan County
Median86.331 counties

Map of counties, 2020

Adams County: 94.8 %Asotin County: 65.4 %Benton County: 77.8 %Chelan County: 74.9 %Clallam County: 83.1 %Clark County: 74.3 %Columbia County: 88.5 %Cowlitz County: 90.4 %Franklin County: 93.2 %Garfield County: 91 %Grant County: 88.8 %Grays Harbor County: 90.2 %Jefferson County: 94.4 %King County: 67.8 %Kitsap County: 89.2 %Kittitas County: 81.4 %Klickitat County: 89.3 %Lewis County: 93.7 %Mason County: 87.4 %Okanogan County: 53.6 %Pend Oreille County: 55 %Pierce County: 69.9 %Skagit County: 97.8 %Snohomish County: 63.9 %Spokane County: 78.1 %Stevens County: 59.8 %Thurston County: 86.3 %Walla Walla County: 81.1 %Whatcom County: 93.2 %Whitman County: 91.5 %Yakima County: 54.1 %
  • Under 65
  • 65 to 78
  • 78 to 86
  • 86 to 89
  • 89 to 93
  • 93 and over
  • No data
%, 2020. 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, 2020

Skagit County: 97.8 %Skagit County97.8Adams County: 94.8 %Adams County94.8Jefferson County: 94.4 %Jefferson County94.4Lewis County: 93.7 %Lewis County93.7Franklin County: 93.2 %Franklin County93.2Whatcom County: 93.2 %Whatcom County93.2Whitman County: 91.5 %Whitman County91.5Garfield County: 91 %Garfield County91Cowlitz County: 90.4 %Cowlitz County90.4Grays Harbor County: 90.2 %Grays Harbor County90.2Klickitat County: 89.3 %Klickitat County89.3Kitsap County: 89.2 %Kitsap County89.2Grant County: 88.8 %Grant County88.8Columbia County: 88.5 %Columbia County88.5Mason County: 87.4 %Mason County87.4Thurston County: 86.3 %Thurston County86.3Clallam County: 83.1 %Clallam County83.1Kittitas County: 81.4 %Kittitas County81.4Walla Walla County: 81.1 %Walla Walla County81.1Spokane County: 78.1 %Spokane County78.1Benton County: 77.8 %Benton County77.8Chelan County: 74.9 %Chelan County74.9Clark County: 74.3 %Clark County74.3Pierce County: 69.9 %Pierce County69.9King County: 67.8 %King County67.8Asotin County: 65.4 %Asotin County65.4Snohomish County: 63.9 %Snohomish County63.9Stevens County: 59.8 %Stevens County59.8Pend Oreille County: 55 %Pend Oreille County55Yakima County: 54.1 %Yakima County54.1Okanogan County: 53.6 %Okanogan County53.6Skagit County: 97.8 %Skagit County97.8Adams County: 94.8 %Adams County94.8Jefferson County: 94.4 %Jefferson County94.4Lewis County: 93.7 %Lewis County93.7Franklin County: 93.2 %Franklin County93.2Whatcom County: 93.2 %Whatcom County93.2Whitman County: 91.5 %Whitman County91.5Garfield County: 91 %Garfield County91Cowlitz County: 90.4 %Cowlitz County90.4Grays Harbor County: 90.2 %Grays Harbor County90.2Klickitat County: 89.3 %Klickitat County89.3Kitsap County: 89.2 %Kitsap County89.2Grant County: 88.8 %Grant County88.8Columbia County: 88.5 %Columbia County88.5Mason County: 87.4 %Mason County87.4Thurston County: 86.3 %Thurston County86.3Clallam County: 83.1 %Clallam County83.1Kittitas County: 81.4 %Kittitas County81.4Walla Walla County: 81.1 %Walla Walla County81.1Spokane County: 78.1 %Spokane County78.1Benton County: 77.8 %Benton County77.8Chelan County: 74.9 %Chelan County74.9Clark County: 74.3 %Clark County74.3Pierce County: 69.9 %Pierce County69.9King County: 67.8 %King County67.8Asotin County: 65.4 %Asotin County65.4Snohomish County: 63.9 %Snohomish County63.9Stevens County: 59.8 %Stevens County59.8Pend Oreille County: 55 %Pend Oreille County55Yakima County: 54.1 %Yakima County54.1Okanogan County: 53.6 %Okanogan County53.6
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2020 (%)Change on 2019
1Skagit County97.8+4.6 pts
2Adams County94.8+0.6 pts
3Jefferson County94.4+0.2 pts
4Lewis County93.7+9.3 pts
5Franklin County93.2+6.7 pts
5Whatcom County93.2+1.2 pts
7Whitman County91.5+2.7 pts
8Garfield County91-1.2 pts
9Cowlitz County90.4+6.8 pts
10Grays Harbor County90.2-2.7 pts
11Klickitat County89.3+7.1 pts
12Kitsap County89.2-2.9 pts
13Grant County88.8+5 pts
14Columbia County88.5+0.3 pts
15Mason County87.4+2.9 pts
16Thurston County86.3+6.8 pts
17Clallam County83.1+5 pts
18Kittitas County81.4+8 pts
19Walla Walla County81.1-0.8 pts
20Spokane County78.1+7.4 pts
21Benton County77.8+2.8 pts
22Chelan County74.9+4.2 pts
23Clark County74.3-1.8 pts
24Pierce County69.9+5.8 pts
25King County67.8+10.8 pts
26Asotin County65.4-4.6 pts
27Snohomish County63.9+1.5 pts
28Stevens County59.8-1.3 pts
29Pend Oreille County55n/a
30Yakima County54.1+5.3 pts
31Okanogan County53.6-3.7 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 2020 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), 2020) [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), 2020. 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=2020. 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), 2020. 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=2020.

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), 2020 [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=2020 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_washington_by_2020,
  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), 2020}},
  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=2020. 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), 2020
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=2020
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/washington-counties?period=2020.
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  -
Embed this chart

Paste this code into a web page or a blog post. The chart shows the latest figures as they are published, with the source and a link back to this page.

Sites that read oEmbed links, such as WordPress, can show the chart when you paste the link to this page.

Use this data in your AI agent

Invokely serves this figure to AI assistants through MCP and to code through a REST API, with the source and citation attached. Ask your assistant:

Rank Counties in Washington by share of days with good air quality (US EPA AQI) using official data, and cite the source.
rank_places {"indicator":"aqi_good_days_share","level":"province","within":"Washington","limit":10}
GET https://invokely.ai/api/v1/rank?indicator=aqi_good_days_share&level=province&within=Washington&limit=10

Connect Claude, ChatGPT or Cursor in one step. The trial answers 25 calls a day without an account.

Questions

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

Skagit County, with 97.8% in 2020, according to EPA.

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

Okanogan County, with 53.6% in 2020.

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 2020 and are not ranked.

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

Counties in Washington: more rankings