Ann Arbor Air Quality in December
Across 2019–2025, Ann Arbor's December air quality had a median AQI of 45 (Good) over 217 monitored days in the Ann Arbor, MI area. 0.0% of December days (0 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 81.1% of days. The cleanest December on record here was 2023 (median AQI 41, 0 days above 100) and the worst was 2019 (median 53, 0 days above 100, peak AQI 83).
- Good: 53.9%
- Moderate: 46.1%
- Unhealthy for Sensitive Groups: 0.0%
- Unhealthy or worse: 0.0%
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How is the air in Ann Arbor in December?
Good on a typical day: median AQI 45 across 2019–2025, with 0.0% of December days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓53.9% of December days were Good (AQI 0–50), 46.1% Moderate (51–100).
- ✓0 days of 217 reached AQI 101+; the December peak was 95.
- ✓Best December: 2023; worst December: 2019.
Frequently asked questions
What is the air quality like in Ann Arbor in December?▾
Across 2019–2025, the median daily AQI in Ann Arbor in December was 45 (Good). 53.9% of days were Good, 46.1% Moderate, and 0.0% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is December a good time for outdoor exercise in Ann Arbor?▾
A typical December day in Ann Arbor sits in the Good range (median AQI 45), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of December days reached AQI 101+ in 2019–2025.
Which pollutant causes Ann Arbor's December air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 81.1% of December days in Ann Arbor. The highest December AQI recorded in 2019–2025 was 95 (Moderate), in 2019.
Ann Arbor December air quality, year by year
Ann Arbor December air quality by year (Ann Arbor, MI, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019worst | 31 | 53 | 0 | 83 | PM2.5 |
| 2020 | 31 | 43 | 0 | 95 | PM2.5 |
| 2021 | 31 | 42 | 0 | 71 | PM2.5 |
| 2022 | 31 | 52 | 0 | 90 | PM2.5 |
| 2023cleanest | 31 | 41 | 0 | 67 | PM2.5 |
| 2024 | 31 | 42 | 0 | 65 | PM2.5 |
| 2025 | 31 | 43 | 0 | 69 | PM2.5 |
What December air means in Ann Arbor
A typical December day in Ann Arbor sits in the Good range (median AQI 45), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of December days reached AQI 101+ in 2019–2025.
December's median AQI of 45 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 December AQI across every EPA metro area (95,590 metro-days, 2019–2025) is 39, so Ann Arbor runs above the national December norm; 0.0% of its December days topped AQI 100 versus 0.7% nationally (about the same).
December is part of Ann Arbor's winter season (December, January, February); the winter page pools all three months.
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 month 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.