Data / Rankings / Share of days with good air quality (US EPA AQI) / Counties in Colorado

Counties in Colorado by share of days with good air quality (US EPA AQI)

Pitkin County had the highest share of days with good air quality (US EPA AQI) of 30 counties in 2014, at 100%. Denver County had the lowest, at 41.6%. The median was 75.6%. Source: EPA.

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Highest100Pitkin County
Lowest41.6Denver County
Median75.630 counties

Map of counties, 2014

Adams County: 60.8 %Alamosa County: 94.5 %Arapahoe County: 71.7 %Archuleta County: 99.7 %Boulder County: 70.6 %Chaffee County: 68.7 %Clear Creek County: 63.3 %Delta County: 99.2 %Denver County: 41.6 %Douglas County: 65.6 %El Paso County: 74.8 %Fremont County: 98.3 %Garfield County: 81.9 %Gunnison County: 84.1 %Jackson County: 93.9 %Jefferson County: 62.5 %La Plata County: 76.4 %Larimer County: 53.7 %Mesa County: 59.2 %Moffat County: 87.4 %Montezuma County: 78.1 %Park County: 68.6 %Pitkin County: 100 %Prowers County: 92.2 %Pueblo County: 88.7 %Rio Blanco County: 72.3 %Routt County: 96.5 %San Juan County: 100 %San Miguel County: 74.8 %Weld County: 65.5 %
  • Under 63
  • 63 to 70
  • 70 to 76
  • 76 to 88
  • 88 to 97
  • 97 and over
  • No data
%, 2014. 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, 2014

Pitkin County: 100 %Pitkin County100San Juan County: 100 %San Juan County100Archuleta County: 99.7 %Archuleta County99.7Delta County: 99.2 %Delta County99.2Fremont County: 98.3 %Fremont County98.3Routt County: 96.5 %Routt County96.5Alamosa County: 94.5 %Alamosa County94.5Jackson County: 93.9 %Jackson County93.9Prowers County: 92.2 %Prowers County92.2Pueblo County: 88.7 %Pueblo County88.7Moffat County: 87.4 %Moffat County87.4Gunnison County: 84.1 %Gunnison County84.1Garfield County: 81.9 %Garfield County81.9Montezuma County: 78.1 %Montezuma County78.1La Plata County: 76.4 %La Plata County76.4El Paso County: 74.8 %El Paso County74.8San Miguel County: 74.8 %San Miguel County74.8Rio Blanco County: 72.3 %Rio Blanco County72.3Arapahoe County: 71.7 %Arapahoe County71.7Boulder County: 70.6 %Boulder County70.6Chaffee County: 68.7 %Chaffee County68.7Park County: 68.6 %Park County68.6Douglas County: 65.6 %Douglas County65.6Weld County: 65.5 %Weld County65.5Clear Creek County: 63.3 %Clear Creek County63.3Jefferson County: 62.5 %Jefferson County62.5Adams County: 60.8 %Adams County60.8Mesa County: 59.2 %Mesa County59.2Larimer County: 53.7 %Larimer County53.7Denver County: 41.6 %Denver County41.6Pitkin County: 100 %Pitkin County100San Juan County: 100 %San Juan County100Archuleta County: 99.7 %Archuleta County99.7Delta County: 99.2 %Delta County99.2Fremont County: 98.3 %Fremont County98.3Routt County: 96.5 %Routt County96.5Alamosa County: 94.5 %Alamosa County94.5Jackson County: 93.9 %Jackson County93.9Prowers County: 92.2 %Prowers County92.2Pueblo County: 88.7 %Pueblo County88.7Moffat County: 87.4 %Moffat County87.4Gunnison County: 84.1 %Gunnison County84.1Garfield County: 81.9 %Garfield County81.9Montezuma County: 78.1 %Montezuma County78.1La Plata County: 76.4 %La Plata County76.4El Paso County: 74.8 %El Paso County74.8San Miguel County: 74.8 %San Miguel County74.8Rio Blanco County: 72.3 %Rio Blanco County72.3Arapahoe County: 71.7 %Arapahoe County71.7Boulder County: 70.6 %Boulder County70.6Chaffee County: 68.7 %Chaffee County68.7Park County: 68.6 %Park County68.6Douglas County: 65.6 %Douglas County65.6Weld County: 65.5 %Weld County65.5Clear Creek County: 63.3 %Clear Creek County63.3Jefferson County: 62.5 %Jefferson County62.5Adams County: 60.8 %Adams County60.8Mesa County: 59.2 %Mesa County59.2Larimer County: 53.7 %Larimer County53.7Denver County: 41.6 %Denver County41.6
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2014 (%)Change on 2013
1Pitkin County100+20.6 pts
1San Juan County100+0.8 pts
3Archuleta County99.7+2.6 pts
4Delta County99.20 pts
5Fremont County98.3+1.5 pts
6Routt County96.5+0.2 pts
7Alamosa County94.5-0.6 pts
8Jackson County93.9+4.6 pts
9Prowers County92.2+2.4 pts
10Pueblo County88.7+0.5 pts
11Moffat County87.4+6.2 pts
12Gunnison County84.1+11 pts
13Garfield County81.9+15.3 pts
14Montezuma County78.1+11 pts
15La Plata County76.4+12.8 pts
16El Paso County74.8+12.3 pts
16San Miguel County74.8+8.8 pts
18Rio Blanco County72.3+21.1 pts
19Arapahoe County71.7+15.3 pts
20Boulder County70.6+7.3 pts
21Chaffee County68.7+28 pts
22Park County68.6+0.8 pts
23Douglas County65.6+0.2 pts
24Weld County65.5+6.3 pts
25Clear Creek County63.3+42 pts
26Jefferson County62.5+5.2 pts
27Adams County60.8+4.1 pts
28Mesa County59.2-2.4 pts
29Larimer County53.7+3.3 pts
30Denver County41.6-3.1 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. 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: 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 Colorado by share of days with good air quality (US EPA AQI), 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: good days as a share of days with an AQI, calculated with stored counts, Counties in Colorado by share of days with good air quality (US EPA AQI), 2014. 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/colorado-counties?period=2014. 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 Colorado by share of days with good air quality (US EPA AQI), 2014. 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/colorado-counties?period=2014.

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 Colorado by share of days with good air quality (US EPA AQI), 2014 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/good-air-quality-days-share/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: good days as a share of days with an AQI, calculated with stored counts: Counties in Colorado by share of days with good air quality (US EPA AQI), 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/good-air-quality-days-share/colorado-counties?period=2014. 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 Colorado by share of days with good air quality (US EPA AQI), 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/good-air-quality-days-share/colorado-counties?period=2014
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/colorado-counties?period=2014.
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  -
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Questions

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

Pitkin County, with 100% in 2014, according to EPA.

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

Denver County, with 41.6% 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: good days as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 10 counties have no value for 2014 and are not ranked.

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

Counties in Colorado: more rankings