Ann Arbor Air Quality in Winter
Across 2019–2025, Ann Arbor's winter (December–February) air quality had a median AQI of 46 (Good) over 632 monitored days in the Ann Arbor, MI area. 0.0% of winter days (0 of 632) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 75.5% of days. The cleanest winter on record here was 2025 (median AQI 37, 0 days above 100) and the worst was 2023 (median 52, 0 days above 100, peak AQI 83).
- Good: 55.7%
- Moderate: 44.3%
- Unhealthy for Sensitive Groups: 0.0%
- Unhealthy or worse: 0.0%
Improve Indoor Air Quality
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How is the air in Ann Arbor in winter?
Good on a typical day: median AQI 46 across 2019–2025, with 0.0% of winter days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓55.7% of winter days were Good (AQI 0–50), 44.3% Moderate (51–100).
- ✓0 days of 632 reached AQI 101+; the winter peak was 95.
- ✓Cleanest month: December; worst month: February.
Frequently asked questions
What is the air quality like in Ann Arbor in winter?▾
Across 2019–2025, the median daily AQI in Ann Arbor in winter was 46 (Good). 55.7% of days were Good, 44.3% Moderate, and 0.0% 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 Ann Arbor?▾
A typical winter day in Ann Arbor sits in the Good range (median AQI 46), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of winter days reached AQI 101+ in 2019–2025.
Which pollutant causes Ann Arbor's winter air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 75.5% of winter days in Ann Arbor. The highest winter AQI recorded in 2019–2025 was 95 (Moderate), in 2023.
Ann Arbor winter air quality, year by year
Ann Arbor winter air quality by year (Ann Arbor, MI, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 90 | 51 | 0 | 89 | PM2.5 |
| 2020 | 91 | 39 | 0 | 95 | PM2.5 |
| 2021 | 90 | 48 | 0 | 82 | PM2.5 |
| 2022 | 90 | 52 | 0 | 90 | PM2.5 |
| 2023worst | 90 | 52 | 0 | 83 | PM2.5 |
| 2024 | 91 | 43 | 0 | 81 | PM2.5 |
| 2025cleanest | 90 | 37 | 0 | 75 | PM2.5 |
What winter air means in Ann Arbor
A typical winter day in Ann Arbor sits in the Good range (median AQI 46), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of winter days reached AQI 101+ in 2019–2025.
Winter's median AQI of 46 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 Winter AQI across every EPA metro area (278,620 metro-days, 2019–2025) is 40, so Ann Arbor runs above the national Winter norm; 0.0% of its Winter days topped AQI 100 versus 0.6% nationally (about the same).
Within the season, December is the cleanest month (median AQI 45, 0.0% of days above 100) and February the worst (median 47, 0.0% 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.