Data / Rankings / Median Air Quality Index (US EPA) / Counties in Colorado

Counties in Colorado by median Air Quality Index (US EPA)

Denver County had the highest median Air Quality Index (US EPA) of 30 counties in 2014, at 53. San Juan County had the lowest, at 10. The median was 45. Source: the U.S. Environmental Protection Agency.

Keep it in a collection in your library.
Highest53Denver County
Lowest10San Juan County
Median4530 counties

Map of counties, 2014

Adams County: 48 indexAlamosa County: 19 indexArapahoe County: 45 indexArchuleta County: 17 indexBoulder County: 45 indexChaffee County: 47 indexClear Creek County: 47 indexDelta County: 21 indexDenver County: 53 indexDouglas County: 44 indexEl Paso County: 45 indexFremont County: 15 indexGarfield County: 44 indexGunnison County: 44 indexJackson County: 40 indexJefferson County: 46 indexLa Plata County: 44 indexLarimer County: 50 indexMesa County: 48 indexMoffat County: 43 indexMontezuma County: 45 indexPark County: 47 indexPitkin County: 12 indexProwers County: 19 indexPueblo County: 28 indexRio Blanco County: 45 indexRoutt County: 15 indexSan Juan County: 10 indexSan Miguel County: 45 indexWeld County: 46 index
  • Under 19
  • 19 to 42
  • 42 to 45
  • 45 to 47
  • 47 and over
  • No data
index, 2014. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2014

Denver County: 53 indexDenver County53Larimer County: 50 indexLarimer County50Adams County: 48 indexAdams County48Mesa County: 48 indexMesa County48Chaffee County: 47 indexChaffee County47Clear Creek County: 47 indexClear Creek County47Park County: 47 indexPark County47Jefferson County: 46 indexJefferson County46Weld County: 46 indexWeld County46Arapahoe County: 45 indexArapahoe County45Boulder County: 45 indexBoulder County45El Paso County: 45 indexEl Paso County45Montezuma County: 45 indexMontezuma County45Rio Blanco County: 45 indexRio Blanco County45San Miguel County: 45 indexSan Miguel County45Douglas County: 44 indexDouglas County44Garfield County: 44 indexGarfield County44Gunnison County: 44 indexGunnison County44La Plata County: 44 indexLa Plata County44Moffat County: 43 indexMoffat County43Jackson County: 40 indexJackson County40Pueblo County: 28 indexPueblo County28Delta County: 21 indexDelta County21Alamosa County: 19 indexAlamosa County19Prowers County: 19 indexProwers County19Archuleta County: 17 indexArchuleta County17Fremont County: 15 indexFremont County15Routt County: 15 indexRoutt County15Pitkin County: 12 indexPitkin County12San Juan County: 10 indexSan Juan County10Denver County: 53 indexDenver County53Larimer County: 50 indexLarimer County50Adams County: 48 indexAdams County48Mesa County: 48 indexMesa County48Chaffee County: 47 indexChaffee County47Clear Creek County: 47 indexClear Creek County47Park County: 47 indexPark County47Jefferson County: 46 indexJefferson County46Weld County: 46 indexWeld County46Arapahoe County: 45 indexArapahoe County45Boulder County: 45 indexBoulder County45El Paso County: 45 indexEl Paso County45Montezuma County: 45 indexMontezuma County45Rio Blanco County: 45 indexRio Blanco County45San Miguel County: 45 indexSan Miguel County45Douglas County: 44 indexDouglas County44Garfield County: 44 indexGarfield County44Gunnison County: 44 indexGunnison County44La Plata County: 44 indexLa Plata County44Moffat County: 43 indexMoffat County43Jackson County: 40 indexJackson County40Pueblo County: 28 indexPueblo County28Delta County: 21 indexDelta County21Alamosa County: 19 indexAlamosa County19Prowers County: 19 indexProwers County19Archuleta County: 17 indexArchuleta County17Fremont County: 15 indexFremont County15Routt County: 15 indexRoutt County15Pitkin County: 12 indexPitkin County12San Juan County: 10 indexSan Juan County10
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties2014
index		Change on 2013
1Denver County53+1
2Larimer County500
3Adams County480
3Mesa County48+1
5Chaffee County47-7
5Clear Creek County47-30
5Park County470
8Jefferson County46-1
8Weld County46-2
10Arapahoe County45-2
10Boulder County45-1
10El Paso County45-2
10Montezuma County45-1
10Rio Blanco County45-5
10San Miguel County45-2
16Douglas County440
16Garfield County44-2
16Gunnison County44-1
16La Plata County44-3
20Moffat County43-1
21Jackson County40-2
22Pueblo County28-1
23Delta County21+2
24Alamosa County19-1
24Prowers County19+1
26Archuleta County170
27Fremont County15-1
27Routt County150
29Pitkin County12-32
30San Juan County10-2

Other periods

About this ranking

Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries.

More on how it is measured
  • The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide).
  • Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.

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. 10 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: median 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: median daily AQI (Counties in Colorado by median Air Quality Index (US EPA), 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: median daily AQI, Counties in Colorado by median Air Quality Index (US EPA), 2014. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/median-air-quality-index/colorado-counties?period=2014. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Counties in Colorado by median Air Quality Index (US EPA), 2014. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/median-air-quality-index/colorado-counties?period=2014.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Counties in Colorado by median Air Quality Index (US EPA), 2014 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/median-air-quality-index/colorado-counties?period=2014 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_colorado_by_2014,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Counties in Colorado by median Air Quality Index (US EPA), 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/median-air-quality-index/colorado-counties?period=2014. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median 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: median daily AQI: Counties in Colorado by median Air Quality Index (US EPA), 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/median-air-quality-index/colorado-counties?period=2014
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/colorado-counties?period=2014.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median 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 median Air Quality Index (US EPA) using official data, and cite the source.
rank_places {"indicator":"aqi_median","level":"province","within":"Colorado","limit":10}
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Questions

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

Denver County, with 53 in 2014, according to the U.S. Environmental Protection Agency.

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

San Juan County, with 10 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: median daily AQI. Retrieved 2026-10-12. 10 counties have no value for 2014 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Colorado: more rankings