Aurora, CO Air Quality in Fall
Across 2019–2025, Aurora's fall (September–November) air quality had a median AQI of 56 (Moderate) over 637 monitored days in the Denver-Aurora-Lakewood, CO area. 3.9% of fall days (25 of 637) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 50.7% of days. The cleanest fall on record here was 2025 (median AQI 51, 1 day above 100) and the worst was 2021 (median 55, 10 days above 100, peak AQI 177).
- Good: 29.4%
- Moderate: 66.7%
- Unhealthy for Sensitive Groups: 3.6%
- Unhealthy or worse: 0.3%
Reduce Indoor Ozone in Aurora
Today's main pollutant in Aurora 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
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How is the air in Aurora in fall?
Moderate on a typical day: median AQI 56 across 2019–2025, with 3.9% of fall days above AQI 100. Ground-level ozone is the main driver.
- ✓29.4% of fall days were Good (AQI 0–50), 66.7% Moderate (51–100).
- ✓25 days of 637 reached AQI 101+; the fall peak was 177.
- ✓Cleanest month: November; worst month: September.
Frequently asked questions
What is the air quality like in Aurora in fall?▾
Across 2019–2025, the median daily AQI in Aurora in fall was 56 (Moderate). 29.4% of days were Good, 66.7% Moderate, and 3.9% reached Unhealthy for Sensitive Groups or worse, based on 637 monitored days in EPA's Air Quality System.
Is fall a good time for outdoor exercise in Aurora?▾
A typical fall day in Aurora is Moderate (median AQI 56): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 26 of fall days (3.9%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Aurora's fall air quality problems?▾
Ground-level ozone set the daily AQI on 50.7% of fall days in Aurora. The highest fall AQI recorded in 2019–2025 was 177 (Unhealthy), in 2021.
Aurora fall air quality, year by year
Aurora fall 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 | 91 | 58 | 1 | 112 | O3 |
| 2020 | 91 | 63 | 8 | 143 | PM2.5 |
| 2021worst | 91 | 55 | 10 | 177 | O3 |
| 2022 | 91 | 53 | 3 | 126 | O3 |
| 2023 | 91 | 56 | 1 | 122 | O3 |
| 2024 | 91 | 58 | 1 | 101 | O3 |
| 2025cleanest | 91 | 51 | 1 | 108 | O3 |
What fall air means in Aurora
A typical fall day in Aurora is Moderate (median AQI 56): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 26 of fall days (3.9%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Fall's median AQI of 56 is below Aurora's whole-year median of 64, making it one of the area's cleaner periods. Nationally, the median Fall AQI across every EPA metro area (296,275 metro-days, 2019–2025) is 40, so Aurora runs above the national Fall norm; 3.9% of its Fall days topped AQI 100 versus 1.5% nationally (above average).
Within the season, November is the cleanest month (median AQI 53, 0.0% of days above 100) and September the worst (median 71, 11.0% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Aurora
The latest EPA AirNow observation puts Aurora's AQI at 43 (O3). The figures above are multi-year season statistics, not today's reading.
View current Aurora 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.