Philadelphia Air Quality in September
Across 2019–2025, Philadelphia's September air quality had a median AQI of 52 (Moderate) over 210 monitored days in the Philadelphia-Camden-Wilmington, PA-NJ-DE-MD area. 1.4% of September days (3 of 210) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 66.7% of days. The cleanest September on record here was 2020 (median AQI 49, 0 days above 100) and the worst was 2023 (median 56, 2 days above 100, peak AQI 105).
- Good: 43.3%
- Moderate: 55.2%
- Unhealthy for Sensitive Groups: 1.4%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Philadelphia
Today's main pollutant in Philadelphia is ground-level ozone (AQI 44). 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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How is the air in Philadelphia in September?
Moderate on a typical day: median AQI 52 across 2019–2025, with 1.4% of September days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓43.3% of September days were Good (AQI 0–50), 55.2% Moderate (51–100).
- ✓3 days of 210 reached AQI 101+; the September peak was 105.
- ✓Best September: 2020; worst September: 2023.
Frequently asked questions
What is the air quality like in Philadelphia in September?▾
Across 2019–2025, the median daily AQI in Philadelphia in September was 52 (Moderate). 43.3% of days were Good, 55.2% Moderate, and 1.4% 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 Philadelphia?▾
A typical September day in Philadelphia is Moderate (median AQI 52): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 71 of September days (1.4%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Philadelphia's September air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 66.7% of September days in Philadelphia. The highest September AQI recorded in 2019–2025 was 105 (Unhealthy for Sensitive Groups), in 2023.
Philadelphia September air quality, year by year
Philadelphia September air quality by year (Philadelphia-Camden-Wilmington, PA-NJ-DE-MD, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 30 | 53 | 1 | 105 | PM2.5 |
| 2020cleanest | 30 | 49 | 0 | 80 | PM2.5 |
| 2021 | 30 | 53 | 0 | 79 | PM2.5 |
| 2022 | 30 | 51 | 0 | 68 | PM2.5 |
| 2023worst | 30 | 56 | 2 | 105 | PM2.5 |
| 2024 | 30 | 49 | 0 | 100 | O3 |
| 2025 | 30 | 55 | 0 | 80 | PM2.5 |
What September air means in Philadelphia
A typical September day in Philadelphia is Moderate (median AQI 52): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 71 of September days (1.4%) 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 52 is below Philadelphia's whole-year median of 56, making it one of the area's cleaner periods. Nationally, the median September AQI across every EPA metro area (100,699 metro-days, 2019–2025) is 43, so Philadelphia runs above the national September norm; 1.4% of its September days topped AQI 100 versus 2.7% nationally (below average).
September is part of Philadelphia's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Philadelphia
The latest EPA AirNow observation puts Philadelphia's AQI at 44 (O3). The figures above are multi-year month statistics, not today's reading.
View current Philadelphia air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Philadelphia-Camden-Wilmington, PA-NJ-DE-MD), 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.