Fort Collins Air Quality in December
Across 2019–2025, Fort Collins's December air quality had a median AQI of 45 (Good) over 217 monitored days in the Fort Collins, CO area. 0.0% of December days (0 of 217) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 71.0% of days. The cleanest December on record here was 2019 (median AQI 44, 0 days above 100) and the worst was 2024 (median 46, 0 days above 100, peak AQI 58).
- Good: 79.3%
- Moderate: 20.7%
- Unhealthy for Sensitive Groups: 0.0%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Fort Collins
Today's main pollutant in Fort Collins is ground-level ozone (AQI 36). 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 is the air in Fort Collins in December?
Good on a typical day: median AQI 45 across 2019–2025, with 0.0% of December days above AQI 100. Ground-level ozone is the main driver.
- ✓79.3% of December days were Good (AQI 0–50), 20.7% Moderate (51–100).
- ✓0 days of 217 reached AQI 101+; the December peak was 88.
- ✓Best December: 2019; worst December: 2024.
Frequently asked questions
What is the air quality like in Fort Collins in December?▾
Across 2019–2025, the median daily AQI in Fort Collins in December was 45 (Good). 79.3% of days were Good, 20.7% Moderate, and 0.0% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is December a good time for outdoor exercise in Fort Collins?▾
A typical December day in Fort Collins sits in the Good range (median AQI 45), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of December days reached AQI 101+ in 2019–2025.
Which pollutant causes Fort Collins's December air quality problems?▾
Ground-level ozone set the daily AQI on 71.0% of December days in Fort Collins. The highest December AQI recorded in 2019–2025 was 88 (Moderate), in 2024.
Fort Collins December air quality, year by year
Fort Collins December air quality by year (Fort Collins, CO, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019cleanest | 31 | 44 | 0 | 60 | O3 |
| 2020 | 31 | 44 | 0 | 57 | O3 |
| 2021 | 31 | 46 | 0 | 67 | O3 |
| 2022 | 31 | 46 | 0 | 88 | O3 |
| 2023 | 31 | 44 | 0 | 67 | O3 |
| 2024worst | 31 | 46 | 0 | 58 | O3 |
| 2025 | 31 | 45 | 0 | 61 | O3 |
What December air means in Fort Collins
A typical December day in Fort Collins sits in the Good range (median AQI 45), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of December days reached AQI 101+ in 2019–2025.
December's median AQI of 45 is below Fort Collins's whole-year median of 51, making it one of the area's cleaner periods. Nationally, the median December AQI across every EPA metro area (95,590 metro-days, 2019–2025) is 39, so Fort Collins runs above the national December norm; 0.0% of its December days topped AQI 100 versus 0.7% nationally (about the same).
December is part of Fort Collins's winter season (December, January, February); the winter page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Fort Collins
The latest EPA AirNow observation puts Fort Collins's AQI at 36 (O3). The figures above are multi-year month 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.