Fort Collins Air Quality in May
Across 2019–2025, Fort Collins's May air quality had a median AQI of 59 (Moderate) over 217 monitored days in the Fort Collins, CO area. 3.2% of May days (7 of 217) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 96.8% of days. The cleanest May on record here was 2021 (median AQI 54, 0 days above 100) and the worst was 2025 (median 67, 4 days above 100, peak AQI 119).
- Good: 33.2%
- Moderate: 63.6%
- Unhealthy for Sensitive Groups: 3.2%
- 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 May?
Moderate on a typical day: median AQI 59 across 2019–2025, with 3.2% of May days above AQI 100. Ground-level ozone is the main driver.
- ✓33.2% of May days were Good (AQI 0–50), 63.6% Moderate (51–100).
- ✓7 days of 217 reached AQI 101+; the May peak was 133.
- ✓Best May: 2021; worst May: 2025.
Frequently asked questions
What is the air quality like in Fort Collins in May?▾
Across 2019–2025, the median daily AQI in Fort Collins in May was 59 (Moderate). 33.2% of days were Good, 63.6% Moderate, and 3.2% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is May a good time for outdoor exercise in Fort Collins?▾
A typical May day in Fort Collins is Moderate (median AQI 59): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 31 of May days (3.2%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Fort Collins's May air quality problems?▾
Ground-level ozone set the daily AQI on 96.8% of May days in Fort Collins. The highest May AQI recorded in 2019–2025 was 133 (Unhealthy for Sensitive Groups), in 2025.
Fort Collins May air quality, year by year
Fort Collins May air quality by year (Fort Collins, CO, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 31 | 58 | 0 | 90 | O3 |
| 2020 | 31 | 52 | 1 | 133 | O3 |
| 2021cleanest | 31 | 54 | 0 | 100 | O3 |
| 2022 | 31 | 54 | 0 | 93 | O3 |
| 2023 | 31 | 67 | 2 | 105 | O3 |
| 2024 | 31 | 67 | 0 | 90 | O3 |
| 2025worst | 31 | 67 | 4 | 119 | O3 |
What May air means in Fort Collins
A typical May day in Fort Collins is Moderate (median AQI 59): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 31 of May days (3.2%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
May's median AQI of 59 is above Fort Collins's whole-year median of 51, making it one of the area's dirtier periods. Nationally, the median May AQI across every EPA metro area (104,064 metro-days, 2019–2025) is 44, so Fort Collins runs above the national May norm; 3.2% of its May days topped AQI 100 versus 1.3% nationally (above average).
May is part of Fort Collins's spring season (March, April, May); the spring 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.