Ann Arbor Best & Worst AQI Days: Air Quality Guide
The worst air quality day on record for Ann Arbor (Ann Arbor, MI area) was June 28, 2023, when the daily AQI reached 218 (Very Unhealthy), set by fine particulate matter (PM2.5), in wildfire smoke season. Across 2,557 monitored days in 2019–2025, 6 of the 10 worst days were Unhealthy (AQI 151+) or worse; 8 of the 10 were driven by fine particulate matter (PM2.5) and 2 by ground-level ozone, and 6 of them fell in 2023. The cleanest day was September 28, 2022 at AQI 12 (Good); the 10 best days span 5 different years.
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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When were Ann Arbor's worst and best air quality days?
Worst: June 28, 2023, AQI 218 (Very Unhealthy, PM2.5). Best: September 28, 2022, AQI 12 (Good). Based on 2,557 EPA-monitored days in the Ann Arbor, MI area, 2019–2025.
- ✓6 of the 10 worst days were Unhealthy (AQI 151+) or worse; the 10th-worst was AQI 129 (Unhealthy for Sensitive Groups).
- ✓Fine particulate matter (PM2.5) drove 8 of the 10 worst days.
- ✓2023 accounts for 6 of the 10 worst days.
Frequently asked questions
What was the worst air quality day in Ann Arbor?▾
June 28, 2023: the Ann Arbor, MI area's daily AQI hit 218 (Very Unhealthy), driven by fine particulate matter (PM2.5), in wildfire smoke season. That is the highest of 2,557 monitored days in 2019–2025.
What was the best air quality day in Ann Arbor?▾
September 28, 2022, with a daily AQI of 12 (Good). The daily AQI is the highest reading from any monitor in the area, so even the cleanest day reflects the area's worst monitor.
What was Ann Arbor's worst air quality day in 2025?▾
June 6, 2025, AQI 152 (Unhealthy), set by fine particulate matter (PM2.5), in wildfire smoke season.
Which pollutant causes Ann Arbor's worst air days?▾
Fine particulate matter (PM2.5) set the AQI on 8 of the 10 worst days; ground-level ozone on 2. The tables above list the defining pollutant for every day.
Ann Arbor's 10 worst air quality days, 2019–2025
Highest daily AQI recorded for the Ann Arbor, MI area (EPA AQS). The daily AQI is the highest reading from any monitor in the area that day.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2023 page) | 218 | Very Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 2 | (2023 page) | 214 | Very Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 3 | (2023 page) | 190 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 4 | (2020 page) | 160 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 5 | (2025 page) | 152 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 6 | (2023 page) | 152 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 7 | (2023 page) | 143 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 8 | (2025 page) | 136 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 9 | (2025 page) | 133 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season |
| 10 | (2023 page) | 129 | Unhealthy for Sensitive Groups | O3 — ground-level ozone |
Worst day of each year in Ann Arbor
The single highest-AQI day in each year on record. Click a year for its full month-by-month statistics.
| Year | Worst day | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 2019 | 89 | Moderate | PM2.5 — fine particulate matter (PM2.5) | |
| 2020 | 160 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2021 | 100 | Moderate | O3 — ground-level ozone, in peak ozone season | |
| 2022 | 101 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season | |
| 2023 | 218 | Very Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2024 | 87 | Moderate | O3 — ground-level ozone | |
| 2025 | 152 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
Ann Arbor's 10 best air quality days, 2019–2025
Lowest daily AQI recorded for the Ann Arbor, MI area. Ties are listed most recent first.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2022 page) | 12 | Good | O3 — ground-level ozone |
| 2 | (2025 page) | 15 | Good | O3 — ground-level ozone |
| 3 | (2025 page) | 16 | Good | O3 — ground-level ozone |
| 4 | (2022 page) | 17 | Good | O3 — ground-level ozone |
| 5 | (2019 page) | 17 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 6 | (2023 page) | 18 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 7 | (2023 page) | 18 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 8 | (2025 page) | 19 | Good | O3 — ground-level ozone |
| 9 | (2024 page) | 19 | Good | O3 — ground-level ozone |
| 10 | (2024 page) | 19 | Good | PM2.5 — fine particulate matter (PM2.5) |
Right now in Ann Arbor
The latest EPA AirNow observation puts Ann Arbor's AQI at 29 (PM2.5). The days above are historical records, 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.