New Haven Air Quality in December
Across 2019–2025, New Haven's December air quality had a median AQI of 43 (Good) over 217 monitored days in the New Haven-Milford, CT area. 0.0% of December days (0 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 72.4% of days. The cleanest December on record here was 2025 (median AQI 34, 0 days above 100) and the worst was 2021 (median 55, 0 days above 100, peak AQI 75).
- Good: 59.0%
- Moderate: 41.0%
- Unhealthy for Sensitive Groups: 0.0%
- Unhealthy or worse: 0.0%
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How is the air in New Haven in December?
Good on a typical day: median AQI 43 across 2019–2025, with 0.0% of December days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓59.0% of December days were Good (AQI 0–50), 41.0% Moderate (51–100).
- ✓0 days of 217 reached AQI 101+; the December peak was 97.
- ✓Best December: 2025; worst December: 2021.
Frequently asked questions
What is the air quality like in New Haven in December?▾
Across 2019–2025, the median daily AQI in New Haven in December was 43 (Good). 59.0% of days were Good, 41.0% Moderate, and 0.0% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is December a good time for outdoor exercise in New Haven?▾
A typical December day in New Haven sits in the Good range (median AQI 43), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of December days reached AQI 101+ in 2019–2025.
Which pollutant causes New Haven's December air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 72.4% of December days in New Haven. The highest December AQI recorded in 2019–2025 was 97 (Moderate), in 2021.
New Haven December air quality, year by year
New Haven December 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 | 31 | 44 | 0 | 97 | PM2.5 |
| 2020 | 31 | 49 | 0 | 96 | PM2.5 |
| 2021worst | 31 | 55 | 0 | 75 | PM2.5 |
| 2022 | 31 | 39 | 0 | 87 | PM2.5 |
| 2023 | 31 | 46 | 0 | 83 | PM2.5 |
| 2024 | 31 | 40 | 0 | 70 | PM2.5 |
| 2025cleanest | 31 | 34 | 0 | 66 | PM2.5 |
What December air means in New Haven
A typical December day in New Haven sits in the Good range (median AQI 43), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of December days reached AQI 101+ in 2019–2025.
December's median AQI of 43 is in line with New Haven's whole-year median of 44, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median December AQI across every EPA metro area (95,590 metro-days, 2019–2025) is 39, so New Haven runs above the national December norm; 0.0% of its December days topped AQI 100 versus 0.7% nationally (about the same).
December is part of New Haven's winter season (December, January, February); the winter 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.