Madison Air Quality in September
Across 2019–2025, Madison's September air quality had a median AQI of 42 (Good) over 210 monitored days in the Madison, WI area. 0.0% of September days (0 of 210) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 51.9% of days. The cleanest September on record here was 2020 (median AQI 35, 0 days above 100) and the worst was 2023 (median 51, 0 days above 100, peak AQI 71).
- Good: 70.5%
- Moderate: 29.5%
- Unhealthy for Sensitive Groups: 0.0%
- Unhealthy or worse: 0.0%
Improve Indoor Air Quality
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How is the air in Madison in September?
Good on a typical day: median AQI 42 across 2019–2025, with 0.0% of September days above AQI 100. Ground-level ozone is the main driver.
- ✓70.5% of September days were Good (AQI 0–50), 29.5% Moderate (51–100).
- ✓0 days of 210 reached AQI 101+; the September peak was 97.
- ✓Best September: 2020; worst September: 2023.
Frequently asked questions
What is the air quality like in Madison in September?▾
Across 2019–2025, the median daily AQI in Madison in September was 42 (Good). 70.5% of days were Good, 29.5% Moderate, and 0.0% reached Unhealthy for Sensitive Groups or worse, based on 210 monitored days in EPA's Air Quality System.
Is September a good time for outdoor exercise in Madison?▾
A typical September day in Madison sits in the Good range (median AQI 42), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of September days reached AQI 101+ in 2019–2025.
Which pollutant causes Madison's September air quality problems?▾
Ground-level ozone set the daily AQI on 51.9% of September days in Madison. The highest September AQI recorded in 2019–2025 was 97 (Moderate), in 2023.
Madison September air quality, year by year
Madison September air quality by year (Madison, WI, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 30 | 37 | 0 | 64 | PM2.5 |
| 2020cleanest | 30 | 35 | 0 | 62 | PM2.5 |
| 2021 | 30 | 43 | 0 | 71 | O3 |
| 2022 | 30 | 39 | 0 | 57 | PM2.5 |
| 2023worst | 30 | 51 | 0 | 71 | PM2.5 |
| 2024 | 30 | 39 | 0 | 93 | O3 |
| 2025 | 30 | 47 | 0 | 97 | O3 |
What September air means in Madison
A typical September day in Madison sits in the Good range (median AQI 42), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of September days reached AQI 101+ in 2019–2025.
September's median AQI of 42 is in line with Madison's whole-year median of 45, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median September AQI across every EPA metro area (100,699 metro-days, 2019–2025) is 43, so Madison runs in line with the national September norm; 0.0% of its September days topped AQI 100 versus 2.7% nationally (below average).
September is part of Madison's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Madison
The latest EPA AirNow observation puts Madison's AQI at 49 (PM2.5). The figures above are multi-year month statistics, not today's reading.
View current Madison air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Madison, 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.