Milwaukee Best & Worst AQI Days: Air Quality Guide
The worst air quality day on record for Milwaukee (Milwaukee-Waukesha-West Allis, WI area) was June 27, 2023, when the daily AQI reached 270 (Very Unhealthy), set by fine particulate matter (PM2.5), in wildfire smoke season. Across 2,557 monitored days in 2019–2025, 10 of the 10 worst days were Unhealthy (AQI 151+) or worse; 5 of the 10 were driven by ground-level ozone and 5 by fine particulate matter (PM2.5), and 4 of them fell in 2023. The cleanest day was October 22, 2025 at AQI 7 (Good); the 10 best days span 2 different years.
Reduce Indoor Ozone in Milwaukee
Today's main pollutant in Milwaukee is ground-level ozone (AQI 32). 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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When were Milwaukee's worst and best air quality days?
Worst: June 27, 2023, AQI 270 (Very Unhealthy, PM2.5). Best: October 22, 2025, AQI 7 (Good). Based on 2,557 EPA-monitored days in the Milwaukee-Waukesha-West Allis, WI area, 2019–2025.
- ✓10 of the 10 worst days were Unhealthy (AQI 151+) or worse; the 10th-worst was AQI 156 (Unhealthy).
- ✓Ground-level ozone drove 5 of the 10 worst days.
- ✓2023 accounts for 4 of the 10 worst days.
Frequently asked questions
What was the worst air quality day in Milwaukee?▾
June 27, 2023: the Milwaukee-Waukesha-West Allis, WI area's daily AQI hit 270 (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 Milwaukee?▾
October 22, 2025, with a daily AQI of 7 (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 Milwaukee's worst air quality day in 2025?▾
July 31, 2025, AQI 175 (Unhealthy), set by fine particulate matter (PM2.5), in wildfire smoke season.
Which pollutant causes Milwaukee's worst air days?▾
Ground-level ozone set the AQI on 5 of the 10 worst days; fine particulate matter (PM2.5) on 5. The tables above list the defining pollutant for every day.
Milwaukee's 10 worst air quality days, 2019–2025
Highest daily AQI recorded for the Milwaukee-Waukesha-West Allis, WI 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) | 270 | Very Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 2 | (2023 page) | 222 | Very Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 3 | (2023 page) | 202 | Very Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 4 | (2023 page) | 180 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 5 | (2025 page) | 175 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 6 | (2020 page) | 169 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 7 | (2024 page) | 161 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 8 | (2025 page) | 160 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 9 | (2022 page) | 159 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 10 | (2024 page) | 156 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
Worst day of each year in Milwaukee
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 | 115 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season | |
| 2020 | 169 | Unhealthy | O3 — ground-level ozone, in peak ozone season | |
| 2021 | 129 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season | |
| 2022 | 159 | Unhealthy | O3 — ground-level ozone, in peak ozone season | |
| 2023 | 270 | Very Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2024 | 161 | Unhealthy | O3 — ground-level ozone, in peak ozone season | |
| 2025 | 175 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
Milwaukee's 10 best air quality days, 2019–2025
Lowest daily AQI recorded for the Milwaukee-Waukesha-West Allis, WI area. Ties are listed most recent first.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2025 page) | 7 | Good | NO2 — nitrogen dioxide |
| 2 | (2025 page) | 10 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 3 | (2025 page) | 11 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 4 | (2024 page) | 11 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 5 | (2025 page) | 12 | Good | NO2 — nitrogen dioxide |
| 6 | (2025 page) | 13 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 7 | (2025 page) | 13 | Good | NO2 — nitrogen dioxide |
| 8 | (2025 page) | 14 | Good | NO2 — nitrogen dioxide |
| 9 | (2025 page) | 15 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 10 | (2025 page) | 16 | Good | PM2.5 — fine particulate matter (PM2.5) |
Right now in Milwaukee
The latest EPA AirNow observation puts Milwaukee's AQI at 32 (O3). The days above are historical records, not today's reading.
View current Milwaukee air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Milwaukee-Waukesha-West Allis, WI), 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.