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

Spokane County had the highest highest daily Air Quality Index (US EPA) of 31 counties in 2023, at 447. Pacific County had the lowest, at 56. The median was 195. Source: the U.S. Environmental Protection Agency.

Highest447Spokane County

Lowest56Pacific County

Median19531 counties

Map of counties, 2023

Under 93
93 to 130
130 to 200
200 to 260
260 to 270
270 and over
No data

index, 2023. 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, 2023

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

Full ranking

Rank	Counties	2023 index	Change on 2022
1	Spokane County	447	+262
2	Whitman County	326	+136
3	Walla Walla County	305	+153
4	Grant County	301	+136
5	Okanogan County	299	+51
6	Stevens County	271	+118
7	Adams County	267	+105
8	Chelan County	266	-24
9	Benton County	261	+110
10	Columbia County	259	+124
11	Franklin County	255	+85
12	Kittitas County	254	+90
13	Garfield County	244	+83
14	Yakima County	233	+75
15	Asotin County	204	+4
16	Pierce County	195	+17
17	Snohomish County	175	-187
18	King County	165	-72
19	Lewis County	159	-39
20	Clark County	153	-22
21	Klickitat County	128	+32
22	Kitsap County	115	-28
23	Mason County	106	-19
24	Clallam County	101	-23
25	Whatcom County	94	-149
26	Skagit County	93	-90
27	Cowlitz County	89	-55
28	Jefferson County	88	-2
29	Thurston County	82	-75
30	Grays Harbor County	80	-32
31	Pacific County	56	n/a

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 2023 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), 2023) [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), 2023. 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=2023. 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), 2023. 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=2023.

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), 2023 [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=2023 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_washington_by_2023,
  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), 2023}},
  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=2023. 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), 2023
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=2023
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/washington-counties?period=2023.
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)?

Spokane County, with 447 in 2023, according to the U.S. Environmental Protection Agency.

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

Pacific County, with 56 in 2023.

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 2023 and are not ranked.