Best Cities for Air Quality in Colorado
Ranking of cities with the cleanest air in Colorado based on AQI data.
Cleanest air in Colorado: Colorado Springs
Of the 4 Colorado metro areas EPA published a full year of AQI data for in 2025, Colorado Springs recorded the highest share of Good-air days: 249 of 365 monitored days (68.2%) at AQI 50 or below, with a median AQI of 46 and 0 days above AQI 100. Its peak reading that year was AQI 97. The pollutant that set the daily AQI most often was ground-level ozone (341 days). The other end of the Colorado list is Denver (28.8% Good days, median AQI 58, 17 days above AQI 100).
| # | City (EPA area) | Good days (2025) | Median AQI | Days over 100 | Peak AQI | AQI now |
|---|---|---|---|---|---|---|
| 1 | Colorado SpringsColorado Springs, CO | 249 / 365 (68.2%) | 46 | 0 | 97 | 31 |
| 2 | Fort CollinsFort Collins, CO | 185 / 365 (50.7%) | 50 | 11 | 119 | 34 |
| 3 | AuroraDenver-Aurora-Lakewood, CO | 105 / 365 (28.8%) | 58 | 17 | 122 | 41 |
| 4 | DenverDenver-Aurora-Lakewood, CO | 105 / 365 (28.8%) | 58 | 17 | 122 | 41 |
Figures are EPA's published annual AQI summaries by metropolitan area (Annual AQI by CBSA, 2019–2025), retrieved 2026-09-07. The daily AQI EPA summarises is the highest value any monitor in the area reported that day, so these are metro-area readings, not statewide or rural ones.
Colorado Springs's air quality year by year
One clean year can be luck — a mild summer, no wildfire smoke. This is every year EPA has published for the Colorado Springs, CO area, so you can see whether Colorado Springs's ranking is durable.
| Year | Days measured | Good days | Median AQI | Days over 100 | Days over 150 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|---|---|
| 2019 | 365 | 249 | 46 | 0 | 0 | 100 | ground-level ozone |
| 2020 | 366 | 241 | 46 | 7 | 1 | 151 | ground-level ozone |
| 2021 | 365 | 224 | 47 | 28 | 0 | 140 | ground-level ozone |
| 2022 | 365 | 249 | 46 | 2 | 0 | 115 | ground-level ozone |
| 2023 | 365 | 240 | 47 | 2 | 1 | 154 | ground-level ozone |
| 2024 | 366 | 202 | 49 | 14 | 2 | 166 | ground-level ozone |
| 2025 | 365 | 249 | 46 | 0 | 0 | 97 | ground-level ozone |
Across 2019–2025, Colorado Springs's air improved: the area's median AQI held near 46 and days above AQI 100 fell from about 12 to 5 per year (comparing the earlier and later halves of the period).
How Colorado compares
Ranked by the median of its metro areas' median AQI in 2025, Colorado is #32 cleanest of the 51 states EPA publishes metro AQI data for, at a median AQI of 50. The cleanest state on that measure is Alaska; the most polluted is Arizona. See the full state air quality rankings.
What this ranking does and does not cover
We track 4 Colorado cities. 4 have a full 2025 EPA record and are ranked above.
EPA's AQI is reported by metropolitan area, and the daily value is the worst reading from any monitor in that area. Rural Colorado — and any town without a regulatory monitor — is not represented here. A high Good-day share means the monitored metro air was clean on most days; it is not a statement about a specific street, and it does not capture short pollution spikes between the daily summaries.