Boston Air Quality in 2019
In 2019, Boston's air quality (Boston-Cambridge-Newton, MA-NH area) had a median daily AQI of 48 (Good) across 365 monitored days. 1 day (0.3%) reached Unhealthy for Sensitive Groups or worse, 201 were Good, and the year's peak AQI was 122 (Unhealthy for Sensitive Groups). Fine particulate matter (PM2.5) set the daily AQI on 257 of those days. The cleanest month of 2019 was May (median AQI 43, 0 days above 100) and the worst was July (median 54, 1 day above 100, peak 122).
- Good: 55.1%
- Moderate: 44.7%
- Unhealthy for Sensitive Groups: 0.3%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Boston
Today's main pollutant in Boston is ground-level ozone (AQI 28). 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 was Boston's air quality in 2019?
Good on a typical day: median AQI 48, with 1 day above AQI 100 out of 365 monitored — the 2nd cleanest of 7 years on record for the area.
- ✓Peak AQI in 2019: 122 (Unhealthy for Sensitive Groups).
- ✓Fine particulate matter (PM2.5) was the main pollutant on 257 days.
- ✓Cleanest month: May; worst: July.
Frequently asked questions
What was the average AQI in Boston in 2019?▾
EPA's Air Quality System puts Boston's (Boston-Cambridge-Newton, MA-NH) median daily AQI for 2019 at 48, which is Good. 1 day were Unhealthy for Sensitive Groups or worse and the year's highest AQI was 122.
Which month had the worst air quality in Boston in 2019?▾
The cleanest month of 2019 was May (median AQI 43, 0 days above 100) and the worst was July (median 54, 1 day above 100, peak 122).
Was 2019 a good or bad year for Boston's air?▾
Among the 7 years EPA has published for the area (2019–2025), 2019 ranks 2nd cleanest by days above AQI 100. 2019's median of 48 is in line with the area's typical annual median of 48.
Boston month by month in 2019
Boston air quality month by month, 2019 (Boston-Cambridge-Newton, MA-NH, EPA AQS daily AQI)
| Month | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| January | 31 | 53 | 0 | 66 | PM2.5 |
| February | 28 | 50 | 0 | 77 | PM2.5 |
| March | 31 | 53 | 0 | 66 | PM2.5 |
| April | 30 | 45 | 0 | 69 | O3 |
| Maycleanest | 31 | 43 | 0 | 63 | O3 |
| June | 30 | 46 | 0 | 84 | O3 |
| Julyworst | 31 | 54 | 1 | 122 | PM2.5 |
| August | 31 | 52 | 0 | 100 | PM2.5 |
| September | 30 | 43 | 0 | 80 | PM2.5 |
| October | 31 | 45 | 0 | 59 | PM2.5 |
| November | 30 | 52 | 0 | 69 | PM2.5 |
| December | 31 | 48 | 0 | 72 | PM2.5 |
How 2019 compares
Among the 7 years EPA has published for the area (2019–2025), 2019 ranks 2nd cleanest by days above AQI 100.
2019's median of 48 is in line with 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 28 (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.