Fort Collins Air Quality in 2021
In 2021, Fort Collins's air quality (Fort Collins, CO area) had a median daily AQI of 54 (Moderate) across 365 monitored days. 50 days (13.7%) reached Unhealthy for Sensitive Groups or worse, 164 were Good, and the year's peak AQI was 159 (Unhealthy). Ground-level ozone set the daily AQI on 298 of those days. The cleanest month of 2021 was January (median AQI 46, 0 days above 100) and the worst was July (median 105, 17 days above 100, peak 159).
- Good: 44.9%
- Moderate: 41.4%
- Unhealthy for Sensitive Groups: 12.6%
- Unhealthy or worse: 1.1%
Reduce Indoor Ozone in Fort Collins
Today's main pollutant in Fort Collins is ground-level ozone (AQI 48). Important: standard HEPA filters do NOT remove ozone — only a purifier with a substantial activated-carbon bed adsorbs it. The biggest wins are cutting indoor sources (gas appliances, certain "ionizer" purifiers) and ventilating when outdoor ozone is low (early morning). A high-carbon unit helps with the gases and VOCs that linger indoors.
Recommended: Levoit Core 300 — True HEPA + activated carbon · CADR ~141 CFM · rooms up to 219 sq ft
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How was Fort Collins's air quality in 2021?
Moderate on a typical day: median AQI 54, with 50 days above AQI 100 out of 365 monitored — the 7th cleanest of 7 years on record for the area.
- ✓Peak AQI in 2021: 159 (Unhealthy).
- ✓Ground-level ozone was the main pollutant on 298 days.
- ✓Cleanest month: January; worst: July.
Frequently asked questions
What was the average AQI in Fort Collins in 2021?▾
EPA's Air Quality System puts Fort Collins's (Fort Collins, CO) median daily AQI for 2021 at 54, which is Moderate. 50 days were Unhealthy for Sensitive Groups or worse and the year's highest AQI was 159.
Which month had the worst air quality in Fort Collins in 2021?▾
The cleanest month of 2021 was January (median AQI 46, 0 days above 100) and the worst was July (median 105, 17 days above 100, peak 159).
Was 2021 a good or bad year for Fort Collins's air?▾
Among the 7 years EPA has published for the area (2019–2025), 2021 ranks 7th cleanest by days above AQI 100 — the worst year on record here. 2021's median of 54 is above the area's typical annual median of 51.
Fort Collins month by month in 2021
Fort Collins air quality month by month, 2021 (Fort Collins, CO, EPA AQS daily AQI)
| Month | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| Januarycleanest | 31 | 46 | 0 | 77 | O3 |
| February | 28 | 49 | 1 | 121 | O3 |
| March | 31 | 50 | 2 | 151 | O3 |
| April | 30 | 54 | 0 | 84 | O3 |
| May | 31 | 54 | 0 | 100 | O3 |
| June | 30 | 77 | 7 | 156 | O3 |
| Julyworst | 31 | 105 | 17 | 159 | O3 |
| August | 31 | 97 | 12 | 147 | O3 |
| September | 30 | 93 | 11 | 143 | O3 |
| October | 31 | 46 | 0 | 74 | O3 |
| November | 30 | 46 | 0 | 75 | O3 |
| December | 31 | 46 | 0 | 67 | O3 |
How 2021 compares
Among the 7 years EPA has published for the area (2019–2025), 2021 ranks 7th cleanest by days above AQI 100 — the worst year on record here.
2021's median of 54 is above the area's typical annual median of 51.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Fort Collins
The latest EPA AirNow observation puts Fort Collins's AQI at 48 (O3). The figures above are multi-year annual statistics, not today's reading.
View current Fort Collins air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Fort Collins, CO), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.