Fort Collins Air Quality in Winter
Across 2019–2025, Fort Collins's winter (December–February) air quality had a median AQI of 47 (Good) over 632 monitored days in the Fort Collins, CO area. 0.2% of winter days (1 of 632) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 66.8% of days. The cleanest winter on record here was 2020 (median AQI 44, 0 days above 100) and the worst was 2021 (median 47, 1 day above 100, peak AQI 121).
- Good: 69.5%
- Moderate: 30.4%
- Unhealthy for Sensitive Groups: 0.2%
- 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 winter?
Good on a typical day: median AQI 47 across 2019–2025, with 0.2% of winter days above AQI 100. Ground-level ozone is the main driver.
- ✓69.5% of winter days were Good (AQI 0–50), 30.4% Moderate (51–100).
- ✓1 day of 632 reached AQI 101+; the winter peak was 121.
- ✓Cleanest month: December; worst month: February.
Frequently asked questions
What is the air quality like in Fort Collins in winter?▾
Across 2019–2025, the median daily AQI in Fort Collins in winter was 47 (Good). 69.5% of days were Good, 30.4% Moderate, and 0.2% reached Unhealthy for Sensitive Groups or worse, based on 632 monitored days in EPA's Air Quality System.
Is winter a good time for outdoor exercise in Fort Collins?▾
A typical winter day in Fort Collins sits in the Good range (median AQI 47), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of winter days reached AQI 101+ in 2019–2025.
Which pollutant causes Fort Collins's winter air quality problems?▾
Ground-level ozone set the daily AQI on 66.8% of winter days in Fort Collins. The highest winter AQI recorded in 2019–2025 was 121 (Unhealthy for Sensitive Groups), in 2021.
Fort Collins winter air quality, year by year
Fort Collins winter air quality by year (Fort Collins, CO, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 90 | 47 | 0 | 75 | O3 |
| 2020cleanest | 91 | 44 | 0 | 61 | O3 |
| 2021worst | 90 | 47 | 1 | 121 | O3 |
| 2022 | 90 | 48 | 0 | 88 | O3 |
| 2023 | 90 | 47 | 0 | 78 | O3 |
| 2024 | 91 | 46 | 0 | 77 | O3 |
| 2025 | 90 | 47 | 0 | 74 | O3 |
What winter air means in Fort Collins
A typical winter day in Fort Collins sits in the Good range (median AQI 47), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of winter days reached AQI 101+ in 2019–2025.
Winter's median AQI of 47 is below Fort Collins's whole-year median of 51, making it one of the area's cleaner periods. Nationally, the median Winter AQI across every EPA metro area (278,620 metro-days, 2019–2025) is 40, so Fort Collins runs above the national Winter norm; 0.2% of its Winter days topped AQI 100 versus 0.6% nationally (about the same).
Within the season, December is the cleanest month (median AQI 45, 0.0% of days above 100) and February the worst (median 49, 0.5% above 100).
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 season 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.