St. Paul Best & Worst AQI Days: Air Quality Guide
The worst air quality day on record for St. Paul (Minneapolis-St. Paul-Bloomington, MN-WI area) was July 29, 2021, when the daily AQI reached 193 (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; 8 of the 10 were driven by fine particulate matter (PM2.5) and 2 by ground-level ozone, and 4 of them fell in 2025. The cleanest day was May 17, 2025 at AQI 19 (Good); the 10 best days span 5 different years.
Reduce Indoor Ozone in St. Paul
Today's main pollutant in St. Paul is ground-level ozone (AQI 25). 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 St. Paul's worst and best air quality days?
Worst: July 29, 2021, AQI 193 (Unhealthy, PM2.5). Best: May 17, 2025, AQI 19 (Good). Based on 2,557 EPA-monitored days in the Minneapolis-St. Paul-Bloomington, MN-WI area, 2019–2025.
- ✓10 of the 10 worst days were Unhealthy (AQI 151+) or worse; the 10th-worst was AQI 164 (Unhealthy).
- ✓Fine particulate matter (PM2.5) drove 8 of the 10 worst days.
- ✓2025 accounts for 4 of the 10 worst days.
Frequently asked questions
What was the worst air quality day in St. Paul?▾
July 29, 2021: the Minneapolis-St. Paul-Bloomington, MN-WI area's daily AQI hit 193 (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 St. Paul?▾
May 17, 2025, with a daily AQI of 19 (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 St. Paul's worst air quality day in 2025?▾
June 3, 2025, AQI 178 (Unhealthy), set by fine particulate matter (PM2.5), in wildfire smoke season.
Which pollutant causes St. Paul'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.
St. Paul's 10 worst air quality days, 2019–2025
Highest daily AQI recorded for the Minneapolis-St. Paul-Bloomington, MN-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 | (2021 page) | 193 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 2 | (2023 page) | 190 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 3 | (2025 page) | 178 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 4 | (2025 page) | 175 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 5 | (2025 page) | 173 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 6 | (2021 page) | 168 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 7 | (2025 page) | 167 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 8 | (2024 page) | 166 | Unhealthy | PM2.5 — fine particulate matter (PM2.5) |
| 9 | (2023 page) | 164 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 10 | (2023 page) | 164 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
Worst day of each year in St. Paul
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 | 122 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season | |
| 2020 | 163 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2021 | 193 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2022 | 96 | Moderate | PM2.5 — fine particulate matter (PM2.5) | |
| 2023 | 190 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2024 | 166 | Unhealthy | PM2.5 — fine particulate matter (PM2.5) | |
| 2025 | 178 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
St. Paul's 10 best air quality days, 2019–2025
Lowest daily AQI recorded for the Minneapolis-St. Paul-Bloomington, MN-WI area. Ties are listed most recent first.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2025 page) | 19 | Good | O3 — ground-level ozone |
| 2 | (2019 page) | 19 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 3 | (2019 page) | 19 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 4 | (2024 page) | 20 | Good | O3 — ground-level ozone |
| 5 | (2019 page) | 20 | Good | PM10 — coarse dust (PM10) |
| 6 | (2025 page) | 21 | Good | O3 — ground-level ozone, in peak ozone season |
| 7 | (2024 page) | 21 | Good | O3 — ground-level ozone |
| 8 | (2021 page) | 21 | Good | O3 — ground-level ozone |
| 9 | (2020 page) | 21 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 10 | (2025 page) | 22 | Good | O3 — ground-level ozone |
Right now in St. Paul
The latest EPA AirNow observation puts St. Paul's AQI at 25 (O3). The days above are historical records, not today's reading.
View current St. Paul air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Minneapolis-St. Paul-Bloomington, MN-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.