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

Prowers County had the highest highest daily Air Quality Index (US EPA) of 31 counties in 2022, at 330. Routt County had the lowest, at 43. The median was 115. Source: the U.S. Environmental Protection Agency.

Highest330Prowers County

Lowest43Routt County

Median11531 counties

Map of counties, 2022

Under 80
80 to 110
110 to 120
120 to 130
130 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	Prowers County	330	-254
2	Archuleta County	227	+134
3	Park County	190	+50
4	Douglas County	169	-8
5	Jefferson County	166	-6
6	Alamosa County	134	+25
7	Weld County	133	-21
8	Arapahoe County	129	-32
8	Boulder County	129	-31
10	Adams County	126	-25
10	Clear Creek County	126	-28
10	Larimer County	126	-33
13	Rio Blanco County	122	-34
14	Pueblo County	121	-17
15	Chaffee County	119	0
16	El Paso County	115	-25
17	Denver County	112	-54
17	Gilpin County	112	-39
19	Garfield County	108	-50
19	Gunnison County	108	+7
19	La Plata County	108	-32
19	Mesa County	108	-31
19	San Miguel County	108	+11
24	Montezuma County	87	-28
25	Delta County	80	-61
25	Grand County	80	-39
27	Fremont County	77	+15
28	San Juan County	75	-4
29	Pitkin County	72	-18
30	Jackson County	71	-19
31	Routt County	43	-25

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. 9 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 Colorado 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 Colorado 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/colorado-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 Colorado 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/colorado-counties?period=2022.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: highest daily AQI, Counties in Colorado 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/colorado-counties?period=2022 (Accessed: 12 October 2026).

BibTeX

@misc{environmental_counties_in_colorado_by_2022,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: highest daily AQI: Counties in Colorado 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/colorado-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 Colorado 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/colorado-counties?period=2022
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/highest-daily-air-quality-index/colorado-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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Rank Counties in Colorado by highest daily Air Quality Index (US EPA) using official data, and cite the source.

rank_places {"indicator":"aqi_max","level":"province","within":"Colorado","limit":10}
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Questions

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

Prowers County, with 330 in 2022, according to the U.S. Environmental Protection Agency.

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

Routt County, with 43 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. 9 counties have no value for 2022 and are not ranked.