Denver Air Quality in October
Across 2019–2025, Denver's October air quality had a median AQI of 54 (Moderate) over 217 monitored days in the Denver-Aurora-Lakewood, CO area. 0.9% of October days (2 of 217) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 41.0% of days. The cleanest October on record here was 2025 (median AQI 50, 0 days above 100) and the worst was 2020 (median 64, 2 days above 100, peak AQI 143).
- Good: 30.4%
- Moderate: 68.7%
- Unhealthy for Sensitive Groups: 0.9%
- 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 October?
Moderate on a typical day: median AQI 54 across 2019–2025, with 0.9% of October days above AQI 100. Ground-level ozone is the main driver.
- ✓30.4% of October days were Good (AQI 0–50), 68.7% Moderate (51–100).
- ✓2 days of 217 reached AQI 101+; the October peak was 143.
- ✓Best October: 2025; worst October: 2020.
Frequently asked questions
What is the air quality like in Denver in October?▾
Across 2019–2025, the median daily AQI in Denver in October was 54 (Moderate). 30.4% of days were Good, 68.7% Moderate, and 0.9% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is October a good time for outdoor exercise in Denver?▾
A typical October day in Denver is Moderate (median AQI 54): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and fewer than 1% of October 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 October air quality problems?▾
Ground-level ozone set the daily AQI on 41.0% of October days in Denver. The highest October AQI recorded in 2019–2025 was 143 (Unhealthy for Sensitive Groups), in 2020.
Denver October air quality, year by year
Denver October 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 | 31 | 54 | 0 | 87 | O3 |
| 2020worst | 31 | 64 | 2 | 143 | PM2.5 |
| 2021 | 31 | 53 | 0 | 87 | O3 |
| 2022 | 31 | 52 | 0 | 74 | O3 |
| 2023 | 31 | 52 | 0 | 78 | O3 |
| 2024 | 31 | 63 | 0 | 91 | PM2.5 |
| 2025cleanest | 31 | 50 | 0 | 67 | O3 |
What October air means in Denver
A typical October day in Denver is Moderate (median AQI 54): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and fewer than 1% of October days reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
October's median AQI of 54 is below Denver's whole-year median of 64, making it one of the area's cleaner periods. Nationally, the median October AQI across every EPA metro area (102,872 metro-days, 2019–2025) is 38, so Denver runs above the national October norm; 0.9% of its October days topped AQI 100 versus 1.3% nationally (about the same).
October is part of Denver's fall season (September, October, November); the fall page pools all three months.
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 month 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.