Louisville Air Quality in September
Across 2019–2025, Louisville's September air quality had a median AQI of 53 (Moderate) over 210 monitored days in the Louisville/Jefferson County, KY-IN area. 4.3% of September days (9 of 210) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 59.0% of days. The cleanest September on record here was 2020 (median AQI 52, 0 days above 100) and the worst was 2025 (median 58, 6 days above 100, peak AQI 140).
- Good: 39.5%
- Moderate: 56.2%
- Unhealthy for Sensitive Groups: 4.3%
- Unhealthy or worse: 0.0%
Extra Protection for Louisville Homes
Air quality in Louisville is moderate (AQI 61), 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.
Recommended: Coway AP-1512HH Mighty — True HEPA + carbon · CADR ~246 CFM · rooms up to 361 sq ft
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How is the air in Louisville in September?
Moderate on a typical day: median AQI 53 across 2019–2025, with 4.3% of September days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓39.5% of September days were Good (AQI 0–50), 56.2% Moderate (51–100).
- ✓9 days of 210 reached AQI 101+; the September peak was 140.
- ✓Best September: 2020; worst September: 2025.
Frequently asked questions
What is the air quality like in Louisville in September?▾
Across 2019–2025, the median daily AQI in Louisville in September was 53 (Moderate). 39.5% of days were Good, 56.2% Moderate, and 4.3% 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 Louisville?▾
A typical September day in Louisville is Moderate (median AQI 53): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 23 of September days (4.3%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Louisville's September air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 59.0% of September days in Louisville. The highest September AQI recorded in 2019–2025 was 140 (Unhealthy for Sensitive Groups), in 2025.
Louisville September air quality, year by year
Louisville September air quality by year (Louisville/Jefferson County, KY-IN, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 30 | 61 | 0 | 97 | O3 |
| 2020cleanest | 30 | 52 | 0 | 64 | PM2.5 |
| 2021 | 30 | 48 | 1 | 112 | PM2.5 |
| 2022 | 30 | 52 | 1 | 105 | PM2.5 |
| 2023 | 30 | 55 | 0 | 74 | PM2.5 |
| 2024 | 30 | 48 | 1 | 108 | O3 |
| 2025worst | 30 | 58 | 6 | 140 | O3 |
What September air means in Louisville
A typical September day in Louisville is Moderate (median AQI 53): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 23 of September days (4.3%) 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 53 is in line with Louisville's whole-year median of 54, 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 Louisville runs above the national September norm; 4.3% of its September days topped AQI 100 versus 2.7% nationally (above average).
September is part of Louisville's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Louisville
The latest EPA AirNow observation puts Louisville's AQI at 61 (PM2.5). The figures above are multi-year month statistics, not today's reading.
View current Louisville air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Louisville/Jefferson County, KY-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.