Worcester Air Quality in December
Across 2019–2025, Worcester's December air quality had a median AQI of 37 (Good) over 217 monitored days in the Worcester, MA-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 58.1% of days. The cleanest December on record here was 2022 (median AQI 33, 0 days above 100) and the worst was 2019 (median 44, 0 days above 100, peak AQI 69).
- Good: 77.0%
- Moderate: 23.0%
- Unhealthy for Sensitive Groups: 0.0%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Worcester
Today's main pollutant in Worcester 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.
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How is the air in Worcester in December?
Good on a typical day: median AQI 37 across 2019–2025, with 0.0% of December days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓77.0% of December days were Good (AQI 0–50), 23.0% Moderate (51–100).
- ✓0 days of 217 reached AQI 101+; the December peak was 69.
- ✓Best December: 2022; worst December: 2019.
Frequently asked questions
What is the air quality like in Worcester in December?▾
Across 2019–2025, the median daily AQI in Worcester in December was 37 (Good). 77.0% of days were Good, 23.0% 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 Worcester?▾
A typical December day in Worcester sits in the Good range (median AQI 37), 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 Worcester's December air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 58.1% of December days in Worcester. The highest December AQI recorded in 2019–2025 was 69 (Moderate), in 2019.
Worcester December air quality, year by year
Worcester December air quality by year (Worcester, MA-CT, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019worst | 31 | 44 | 0 | 69 | PM2.5 |
| 2020 | 31 | 41 | 0 | 63 | PM2.5 |
| 2021 | 31 | 42 | 0 | 60 | PM2.5 |
| 2022cleanest | 31 | 33 | 0 | 68 | PM2.5 |
| 2023 | 31 | 36 | 0 | 61 | O3 |
| 2024 | 31 | 34 | 0 | 63 | O3 |
| 2025 | 31 | 34 | 0 | 55 | O3 |
What December air means in Worcester
A typical December day in Worcester sits in the Good range (median AQI 37), 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 37 is below Worcester's whole-year median of 43, making it one of the area's cleaner periods. Nationally, the median December AQI across every EPA metro area (95,590 metro-days, 2019–2025) is 39, so Worcester runs in line with the national December norm; 0.0% of its December days topped AQI 100 versus 0.7% nationally (about the same).
December is part of Worcester's winter season (December, January, February); the winter page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Worcester
The latest EPA AirNow observation puts Worcester's AQI at 32 (O3). The figures above are multi-year month statistics, not today's reading.
View current Worcester air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Worcester, MA-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.