Aurora, CO Air Quality in September
Across 2019–2025, Aurora's September air quality had a median AQI of 71 (Moderate) over 210 monitored days in the Denver-Aurora-Lakewood, CO area. 11.0% of September days (23 of 210) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 81.0% of days. The cleanest September on record here was 2025 (median AQI 60, 1 day above 100) and the worst was 2021 (median 73, 10 days above 100, peak AQI 177).
- Good: 17.6%
- Moderate: 71.4%
- Unhealthy for Sensitive Groups: 10.0%
- Unhealthy or worse: 1.0%
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 September?
Moderate on a typical day: median AQI 71 across 2019–2025, with 11.0% of September days above AQI 100. Ground-level ozone is the main driver.
- ✓17.6% of September days were Good (AQI 0–50), 71.4% Moderate (51–100).
- ✓23 days of 210 reached AQI 101+; the September peak was 177.
- ✓Best September: 2025; worst September: 2021.
Frequently asked questions
What is the air quality like in Aurora in September?▾
Across 2019–2025, the median daily AQI in Aurora in September was 71 (Moderate). 17.6% of days were Good, 71.4% Moderate, and 11.0% reached Unhealthy for Sensitive Groups or worse, based on 210 monitored days in EPA's Air Quality System.
Is September a good time for outdoor exercise in Aurora?▾
A typical September day in Aurora is Moderate (median AQI 71): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 9 of September days (11.0%) 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 September air quality problems?▾
Ground-level ozone set the daily AQI on 81.0% of September days in Aurora. The highest September AQI recorded in 2019–2025 was 177 (Unhealthy), in 2021.
Aurora September air quality, year by year
Aurora September 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 | 30 | 64 | 1 | 112 | O3 |
| 2020 | 30 | 79 | 6 | 136 | O3 |
| 2021worst | 30 | 73 | 10 | 177 | O3 |
| 2022 | 30 | 69 | 3 | 126 | O3 |
| 2023 | 30 | 71 | 1 | 122 | O3 |
| 2024 | 30 | 69 | 1 | 101 | O3 |
| 2025cleanest | 30 | 60 | 1 | 108 | O3 |
What September air means in Aurora
A typical September day in Aurora is Moderate (median AQI 71): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 9 of September days (11.0%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
September's median AQI of 71 is above Aurora's whole-year median of 64, making it one of the area's dirtier periods. Nationally, the median September AQI across every EPA metro area (100,699 metro-days, 2019–2025) is 43, so Aurora runs above the national September norm; 11.0% of its September days topped AQI 100 versus 2.7% nationally (above average).
September is part of Aurora's fall season (September, October, November); the fall page pools all three months.
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 month 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.