Allentown Air Quality in September
Across 2019–2025, Allentown's September air quality had a median AQI of 41 (Good) over 210 monitored days in the Allentown-Bethlehem-Easton, PA-NJ area. 0.5% of September days (1 of 210) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 56.7% of days. The cleanest September on record here was 2020 (median AQI 39, 0 days above 100) and the worst was 2024 (median 38, 1 day above 100, peak AQI 101).
- Good: 75.7%
- Moderate: 23.8%
- Unhealthy for Sensitive Groups: 0.5%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Allentown
Today's main pollutant in Allentown 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 Allentown in September?
Good on a typical day: median AQI 41 across 2019–2025, with 0.5% of September days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓75.7% of September days were Good (AQI 0–50), 23.8% Moderate (51–100).
- ✓1 day of 210 reached AQI 101+; the September peak was 101.
- ✓Best September: 2020; worst September: 2024.
Frequently asked questions
What is the air quality like in Allentown in September?▾
Across 2019–2025, the median daily AQI in Allentown in September was 41 (Good). 75.7% of days were Good, 23.8% Moderate, and 0.5% 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 Allentown?▾
A typical September day in Allentown sits in the Good range (median AQI 41), 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 Allentown's September air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 56.7% of September days in Allentown. The highest September AQI recorded in 2019–2025 was 101 (Unhealthy for Sensitive Groups), in 2024.
Allentown September air quality, year by year
Allentown September air quality by year (Allentown-Bethlehem-Easton, PA-NJ, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 30 | 48 | 0 | 77 | PM2.5 |
| 2020cleanest | 30 | 39 | 0 | 67 | PM2.5 |
| 2021 | 30 | 43 | 0 | 68 | PM2.5 |
| 2022 | 30 | 42 | 0 | 58 | PM2.5 |
| 2023 | 30 | 42 | 0 | 61 | PM2.5 |
| 2024worst | 30 | 38 | 1 | 101 | O3 |
| 2025 | 30 | 44 | 0 | 58 | O3 |
What September air means in Allentown
A typical September day in Allentown sits in the Good range (median AQI 41), 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 41 is below Allentown's whole-year median of 46, 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 Allentown runs in line with the national September norm; 0.5% of its September days topped AQI 100 versus 2.7% nationally (below average).
September is part of Allentown's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Allentown
The latest EPA AirNow observation puts Allentown's AQI at 44 (O3). The figures above are multi-year month statistics, not today's reading.
View current Allentown air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Allentown-Bethlehem-Easton, PA-NJ), 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.