Boston Air Quality in 2025
In 2025, Boston's air quality (Boston-Cambridge-Newton, MA-NH area) had a median daily AQI of 44 (Good) across 365 monitored days. 5 days (1.4%) reached Unhealthy for Sensitive Groups or worse, 259 were Good, and the year's peak AQI was 150 (Unhealthy for Sensitive Groups). Ground-level ozone set the daily AQI on 220 of those days. The cleanest month of 2025 was October (median AQI 33, 0 days above 100) and the worst was June (median 55, 2 days above 100, peak 133).
- Good: 71.0%
- Moderate: 27.7%
- Unhealthy for Sensitive Groups: 1.4%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Boston
Today's main pollutant in Boston 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.
Recommended: Levoit Core 300 — True HEPA + activated carbon · CADR ~141 CFM · rooms up to 219 sq ft
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How was Boston's air quality in 2025?
Good on a typical day: median AQI 44, with 5 days above AQI 100 out of 365 monitored — the 4th cleanest of 7 years on record for the area.
- ✓Peak AQI in 2025: 150 (Unhealthy for Sensitive Groups).
- ✓Ground-level ozone was the main pollutant on 220 days.
- ✓Cleanest month: October; worst: June.
Frequently asked questions
What was the average AQI in Boston in 2025?▾
EPA's Air Quality System puts Boston's (Boston-Cambridge-Newton, MA-NH) median daily AQI for 2025 at 44, which is Good. 5 days were Unhealthy for Sensitive Groups or worse and the year's highest AQI was 150.
Which month had the worst air quality in Boston in 2025?▾
The cleanest month of 2025 was October (median AQI 33, 0 days above 100) and the worst was June (median 55, 2 days above 100, peak 133).
Was 2025 a good or bad year for Boston's air?▾
Among the 7 years EPA has published for the area (2019–2025), 2025 ranks 4th cleanest by days above AQI 100. 2025's median of 44 is below the area's typical annual median of 48.
Boston month by month in 2025
Boston air quality month by month, 2025 (Boston-Cambridge-Newton, MA-NH, EPA AQS daily AQI)
| Month | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| January | 31 | 43 | 0 | 65 | PM2.5 |
| February | 28 | 43 | 0 | 61 | O3 |
| March | 31 | 45 | 0 | 61 | O3 |
| April | 30 | 47 | 0 | 84 | O3 |
| May | 31 | 44 | 0 | 58 | O3 |
| Juneworst | 30 | 55 | 2 | 133 | PM2.5 |
| July | 31 | 52 | 1 | 106 | O3 |
| August | 31 | 47 | 2 | 150 | O3 |
| September | 30 | 39 | 0 | 55 | O3 |
| Octobercleanest | 31 | 33 | 0 | 74 | O3 |
| November | 30 | 36 | 0 | 68 | PM2.5 |
| December | 31 | 41 | 0 | 69 | PM2.5 |
How 2025 compares
Among the 7 years EPA has published for the area (2019–2025), 2025 ranks 4th cleanest by days above AQI 100.
2025's median of 44 is below the area's typical annual median of 48.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Boston
The latest EPA AirNow observation puts Boston's AQI at 33 (O3). The figures above are multi-year annual statistics, not today's reading.
View current Boston 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.