Indianapolis Air Quality in September
Across 2019–2025, Indianapolis's September air quality had a median AQI of 57 (Moderate) over 210 monitored days in the Indianapolis-Carmel-Anderson, IN area. 2.9% of September days (6 of 210) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 77.1% of days. The cleanest September on record here was 2024 (median AQI 52, 0 days above 100) and the worst was 2025 (median 62, 4 days above 100, peak AQI 122).
- Good: 23.8%
- Moderate: 73.3%
- Unhealthy for Sensitive Groups: 2.9%
- Unhealthy or worse: 0.0%
Extra Protection for Indianapolis Homes
Air quality in Indianapolis is moderate (AQI 55), with fine particles (PM2.5) the main concern. A True-HEPA purifier gives sensitive groups — kids, seniors and anyone with asthma or allergies — cleaner air indoors on days like today.
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How is the air in Indianapolis in September?
Moderate on a typical day: median AQI 57 across 2019–2025, with 2.9% of September days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓23.8% of September days were Good (AQI 0–50), 73.3% Moderate (51–100).
- ✓6 days of 210 reached AQI 101+; the September peak was 122.
- ✓Best September: 2024; worst September: 2025.
Frequently asked questions
What is the air quality like in Indianapolis in September?▾
Across 2019–2025, the median daily AQI in Indianapolis in September was 57 (Moderate). 23.8% of days were Good, 73.3% Moderate, and 2.9% 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 Indianapolis?▾
A typical September day in Indianapolis is Moderate (median AQI 57): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 34 of September days (2.9%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Indianapolis's September air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 77.1% of September days in Indianapolis. The highest September AQI recorded in 2019–2025 was 122 (Unhealthy for Sensitive Groups), in 2025.
Indianapolis September air quality, year by year
Indianapolis September air quality by year (Indianapolis-Carmel-Anderson, IN, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 30 | 60 | 1 | 119 | PM2.5 |
| 2020 | 30 | 55 | 0 | 66 | PM2.5 |
| 2021 | 30 | 58 | 1 | 101 | PM2.5 |
| 2022 | 30 | 53 | 0 | 84 | PM2.5 |
| 2023 | 30 | 56 | 0 | 86 | PM2.5 |
| 2024cleanest | 30 | 52 | 0 | 90 | O3 |
| 2025worst | 30 | 62 | 4 | 122 | PM2.5 |
What September air means in Indianapolis
A typical September day in Indianapolis is Moderate (median AQI 57): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 34 of September days (2.9%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
September's median AQI of 57 is in line with Indianapolis's whole-year median of 56, 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 Indianapolis runs above the national September norm; 2.9% of its September days topped AQI 100 versus 2.7% nationally (about the same).
September is part of Indianapolis's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Indianapolis
The latest EPA AirNow observation puts Indianapolis's AQI at 55 (PM2.5). The figures above are multi-year month statistics, not today's reading.
View current Indianapolis air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Indianapolis-Carmel-Anderson, IN), 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.