Denver Air Quality in Winter
Across 2019–2025, Denver's winter (December–February) air quality had a median AQI of 55 (Moderate) over 632 monitored days in the Denver-Aurora-Lakewood, CO area. 0.3% of winter days (2 of 632) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 42.9% of days. The cleanest winter on record here was 2025 (median AQI 52, 0 days above 100) and the worst was 2020 (median 54, 1 day above 100, peak AQI 103).
- Good: 32.9%
- Moderate: 66.8%
- Unhealthy for Sensitive Groups: 0.3%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Denver
Today's main pollutant in Denver is ground-level ozone (AQI 43). 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
As an Amazon Associate, we earn from qualifying purchases.
How is the air in Denver in winter?
Moderate on a typical day: median AQI 55 across 2019–2025, with 0.3% of winter days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓32.9% of winter days were Good (AQI 0–50), 66.8% Moderate (51–100).
- ✓2 days of 632 reached AQI 101+; the winter peak was 109.
- ✓Cleanest month: December; worst month: January.
Frequently asked questions
What is the air quality like in Denver in winter?▾
Across 2019–2025, the median daily AQI in Denver in winter was 55 (Moderate). 32.9% of days were Good, 66.8% Moderate, and 0.3% 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 Denver?▾
A typical winter day in Denver is Moderate (median AQI 55): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and fewer than 1% of winter days reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Denver's winter air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 42.9% of winter days in Denver. The highest winter AQI recorded in 2019–2025 was 109 (Unhealthy for Sensitive Groups), in 2020.
Denver winter air quality, year by year
Denver winter air quality by year (Denver-Aurora-Lakewood, CO, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 90 | 60 | 0 | 99 | PM2.5 |
| 2020worst | 91 | 54 | 1 | 103 | NO2 |
| 2021 | 90 | 53 | 1 | 109 | NO2 |
| 2022 | 90 | 56 | 0 | 84 | PM2.5 |
| 2023 | 90 | 56 | 0 | 89 | PM2.5 |
| 2024 | 91 | 54 | 0 | 93 | PM2.5 |
| 2025cleanest | 90 | 52 | 0 | 86 | PM2.5 |
What winter air means in Denver
A typical winter day in Denver is Moderate (median AQI 55): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and fewer than 1% of winter days reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Winter's median AQI of 55 is below Denver's whole-year median of 64, 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 Denver runs above the national Winter norm; 0.3% of its Winter days topped AQI 100 versus 0.6% nationally (about the same).
Within the season, December is the cleanest month (median AQI 52, 0.0% of days above 100) and January the worst (median 56, 0.9% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Denver
The latest EPA AirNow observation puts Denver's AQI at 43 (O3). The figures above are multi-year season statistics, not today's reading.
View current Denver air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Denver-Aurora-Lakewood, 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.