New Haven Air Quality in September
Across 2019–2025, New Haven's September air quality had a median AQI of 40 (Good) over 210 monitored days in the New Haven-Milford, CT area. 1.0% of September days (2 of 210) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 58.6% of days. The cleanest September on record here was 2024 (median AQI 37, 0 days above 100) and the worst was 2023 (median 47, 1 day above 100, peak AQI 101).
- Good: 79.0%
- Moderate: 20.0%
- Unhealthy for Sensitive Groups: 1.0%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in New Haven
Today's main pollutant in New Haven is ground-level ozone (AQI 32). 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
As an Amazon Associate, we earn from qualifying purchases.
How is the air in New Haven in September?
Good on a typical day: median AQI 40 across 2019–2025, with 1.0% of September days above AQI 100. Ground-level ozone is the main driver.
- ✓79.0% of September days were Good (AQI 0–50), 20.0% Moderate (51–100).
- ✓2 days of 210 reached AQI 101+; the September peak was 126.
- ✓Best September: 2024; worst September: 2023.
Frequently asked questions
What is the air quality like in New Haven in September?▾
Across 2019–2025, the median daily AQI in New Haven in September was 40 (Good). 79.0% of days were Good, 20.0% Moderate, and 1.0% 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 New Haven?▾
A typical September day in New Haven sits in the Good range (median AQI 40), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 100 of September days (1.0%) reached AQI 101+ in 2019–2025.
Which pollutant causes New Haven's September air quality problems?▾
Ground-level ozone set the daily AQI on 58.6% of September days in New Haven. The highest September AQI recorded in 2019–2025 was 126 (Unhealthy for Sensitive Groups), in 2023.
New Haven September air quality, year by year
New Haven September air quality by year (New Haven-Milford, CT, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 30 | 38 | 1 | 126 | O3 |
| 2020 | 30 | 38 | 0 | 77 | PM2.5 |
| 2021 | 30 | 42 | 0 | 58 | PM2.5 |
| 2022 | 30 | 41 | 0 | 97 | O3 |
| 2023worst | 30 | 47 | 1 | 101 | PM2.5 |
| 2024cleanest | 30 | 37 | 0 | 61 | O3 |
| 2025 | 30 | 40 | 0 | 97 | O3 |
What September air means in New Haven
A typical September day in New Haven sits in the Good range (median AQI 40), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 100 of September days (1.0%) reached AQI 101+ in 2019–2025.
September's median AQI of 40 is below New Haven's whole-year median of 44, 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 New Haven runs in line with the national September norm; 1.0% of its September days topped AQI 100 versus 2.7% nationally (below average).
September is part of New Haven's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in New Haven
The latest EPA AirNow observation puts New Haven's AQI at 32 (O3). The figures above are multi-year month statistics, not today's reading.
View current New Haven air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (New Haven-Milford, CT), 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.