Ann Arbor Air Quality in Fall
Across 2019–2025, Ann Arbor's fall (September–November) air quality had a median AQI of 41 (Good) over 637 monitored days in the Ann Arbor, MI area. 0.3% of fall days (2 of 637) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 61.9% of days. The cleanest fall on record here was 2024 (median AQI 37, 0 days above 100) and the worst was 2025 (median 36, 2 days above 100, peak AQI 108).
- Good: 68.6%
- Moderate: 31.1%
- Unhealthy for Sensitive Groups: 0.3%
- Unhealthy or worse: 0.0%
Improve Indoor Air Quality
Even with good outdoor air in Ann Arbor, indoor PM2.5, dust and allergens build up. A True-HEPA purifier keeps a bedroom or office consistently clean.
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How is the air in Ann Arbor in fall?
Good on a typical day: median AQI 41 across 2019–2025, with 0.3% of fall days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓68.6% of fall days were Good (AQI 0–50), 31.1% Moderate (51–100).
- ✓2 days of 637 reached AQI 101+; the fall peak was 108.
- ✓Cleanest month: October; worst month: September.
Frequently asked questions
What is the air quality like in Ann Arbor in fall?▾
Across 2019–2025, the median daily AQI in Ann Arbor in fall was 41 (Good). 68.6% of days were Good, 31.1% Moderate, and 0.3% 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 Ann Arbor?▾
A typical fall day in Ann Arbor sits in the Good range (median AQI 41), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of fall days reached AQI 101+ in 2019–2025.
Which pollutant causes Ann Arbor's fall air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 61.9% of fall days in Ann Arbor. The highest fall AQI recorded in 2019–2025 was 108 (Unhealthy for Sensitive Groups), in 2025.
Ann Arbor fall air quality, year by year
Ann Arbor fall air quality by year (Ann Arbor, MI, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 91 | 42 | 0 | 78 | PM2.5 |
| 2020 | 91 | 38 | 0 | 98 | PM2.5 |
| 2021 | 91 | 41 | 0 | 67 | PM2.5 |
| 2022 | 91 | 49 | 0 | 98 | PM2.5 |
| 2023 | 91 | 42 | 0 | 77 | PM2.5 |
| 2024cleanest | 91 | 37 | 0 | 80 | O3 |
| 2025worst | 91 | 36 | 2 | 108 | O3 |
What fall air means in Ann Arbor
A typical fall day in Ann Arbor sits in the Good range (median AQI 41), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of fall days reached AQI 101+ in 2019–2025.
Fall's median AQI of 41 is in line with Ann Arbor's whole-year median of 44, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median Fall AQI across every EPA metro area (296,275 metro-days, 2019–2025) is 40, so Ann Arbor runs in line with the national Fall norm; 0.3% of its Fall days topped AQI 100 versus 1.5% nationally (below average).
Within the season, October is the cleanest month (median AQI 36, 0.0% of days above 100) and September the worst (median 43, 1.0% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Ann Arbor
The latest EPA AirNow observation puts Ann Arbor's AQI at 29 (PM2.5). The figures above are multi-year season statistics, not today's reading.
View current Ann Arbor air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Ann Arbor, MI), 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.