Counties in Washington by highest daily Air Quality Index (US EPA)

Snohomish County had the highest highest daily Air Quality Index (US EPA) of 31 counties in 2022, at 362. Pend Oreille County had the lowest, at 81. The median was 162. Source: the U.S. Environmental Protection Agency.

Highest362Snohomish County

Lowest81Pend Oreille County

Median16231 counties

Map of counties, 2022

Under 130
130 to 150
150 to 160
160 to 180
180 to 200
200 and over
No data

index, 2022. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2022

index. Source: EPA, EPA AirData annual AQI by county: highest daily AQI. Retrieved 2026-10-12.

Full ranking

Rank	Counties	2022 index	Change on 2021
1	Snohomish County	362	+225
2	Chelan County	290	+95
3	Okanogan County	248	-106
4	Whatcom County	243	+114
5	King County	237	+60
6	Asotin County	200	-33
7	Lewis County	198	+127
8	Whitman County	190	-28
9	Spokane County	185	-10
10	Skagit County	183	+82
11	Pierce County	178	+84
12	Clark County	175	+77
13	Franklin County	170	+86
14	Grant County	165	-37
15	Kittitas County	164	-9
16	Adams County	162	-29
17	Garfield County	161	-63
18	Yakima County	158	-52
19	Thurston County	157	+94
20	Stevens County	153	-70
21	Walla Walla County	152	-20
22	Benton County	151	-29
23	Cowlitz County	144	+80
24	Kitsap County	143	+30
25	Columbia County	135	-37
26	Mason County	125	+55
27	Clallam County	124	+43
28	Grays Harbor County	112	+30
29	Klickitat County	96	+20
30	Jefferson County	90	+11
31	Pend Oreille County	81	-115

Other periods

About this ranking

Highest daily Air Quality Index (AQI) value recorded in a US county during the year, from the EPA AirData annual summaries. Values above 500 are beyond the AQI scale and are published as EPA computes them.

A single day decides the value, so one wildfire or dust event can set it. Dust from the dry Owens Lake bed puts Inyo and Mono counties in California in the thousands. 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 2022 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: highest daily AQI. 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: highest daily AQI (Counties in Washington by highest daily Air Quality Index (US EPA), 2022) [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: highest daily AQI, Counties in Washington by highest daily Air Quality Index (US EPA), 2022. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/washington-counties?period=2022. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: highest daily AQI. Counties in Washington by highest daily Air Quality Index (US EPA), 2022. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/washington-counties?period=2022.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: highest daily AQI, Counties in Washington by highest daily Air Quality Index (US EPA), 2022 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/highest-daily-air-quality-index/washington-counties?period=2022 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_washington_by_2022,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: highest daily AQI: Counties in Washington by highest daily Air Quality Index (US EPA), 2022}},
  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/highest-daily-air-quality-index/washington-counties?period=2022. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest daily AQI. 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: highest daily AQI: Counties in Washington by highest daily Air Quality Index (US EPA), 2022
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/highest-daily-air-quality-index/washington-counties?period=2022
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/washington-counties?period=2022.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: highest daily AQI. 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 highest daily Air Quality Index (US EPA)?

Snohomish County, with 362 in 2022, according to the U.S. Environmental Protection Agency.

Which county has the lowest highest daily Air Quality Index (US EPA)?

Pend Oreille County, with 81 in 2022.

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: highest daily AQI. Retrieved 2026-10-12. 3 counties have no value for 2022 and are not ranked.