Cambridge Air Quality in Winter
Across 2019–2025, Cambridge's winter (December–February) air quality had a median AQI of 48 (Good) over 632 monitored days in the Boston-Cambridge-Newton, MA-NH area. 0.0% of winter days (0 of 632) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 76.6% of days. The cleanest winter on record here was 2024 (median AQI 42, 0 days above 100) and the worst was 2022 (median 53, 0 days above 100, peak AQI 84).
- Good: 53.8%
- Moderate: 46.2%
- Unhealthy for Sensitive Groups: 0.0%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Cambridge
Today's main pollutant in Cambridge is ground-level ozone (AQI 33). 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 Cambridge in winter?
Good on a typical day: median AQI 48 across 2019–2025, with 0.0% of winter days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓53.8% of winter days were Good (AQI 0–50), 46.2% Moderate (51–100).
- ✓0 days of 632 reached AQI 101+; the winter peak was 89.
- ✓Cleanest month: December; worst month: February.
Frequently asked questions
What is the air quality like in Cambridge in winter?▾
Across 2019–2025, the median daily AQI in Cambridge in winter was 48 (Good). 53.8% of days were Good, 46.2% Moderate, and 0.0% reached Unhealthy for Sensitive Groups or worse, based on 632 monitored days in EPA's Air Quality System.
Is winter a good time for outdoor exercise in Cambridge?▾
A typical winter day in Cambridge sits in the Good range (median AQI 48), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of winter days reached AQI 101+ in 2019–2025.
Which pollutant causes Cambridge's winter air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 76.6% of winter days in Cambridge. The highest winter AQI recorded in 2019–2025 was 89 (Moderate), in 2022.
Cambridge winter air quality, year by year
Cambridge winter air quality by year (Boston-Cambridge-Newton, MA-NH, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 90 | 51 | 0 | 77 | PM2.5 |
| 2020 | 91 | 51 | 0 | 81 | PM2.5 |
| 2021 | 90 | 48 | 0 | 89 | PM2.5 |
| 2022worst | 90 | 53 | 0 | 84 | PM2.5 |
| 2023 | 90 | 52 | 0 | 74 | PM2.5 |
| 2024cleanest | 91 | 42 | 0 | 73 | PM2.5 |
| 2025 | 90 | 43 | 0 | 69 | PM2.5 |
What winter air means in Cambridge
A typical winter day in Cambridge sits in the Good range (median AQI 48), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of winter days reached AQI 101+ in 2019–2025.
Winter's median AQI of 48 is in line with Cambridge's whole-year median of 48, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median Winter AQI across every EPA metro area (278,620 metro-days, 2019–2025) is 40, so Cambridge runs above the national Winter norm; 0.0% of its Winter days topped AQI 100 versus 0.6% nationally (about the same).
Within the season, December is the cleanest month (median AQI 48, 0.0% of days above 100) and February the worst (median 50, 0.0% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Cambridge
The latest EPA AirNow observation puts Cambridge's AQI at 33 (O3). The figures above are multi-year season statistics, not today's reading.
View current Cambridge air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Boston-Cambridge-Newton, MA-NH), 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.