Boston Air Quality in October
Across 2019–2025, Boston's October air quality had a median AQI of 42 (Good) over 217 monitored days in the Boston-Cambridge-Newton, MA-NH area. 1.0% of October days (2 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 70.5% of days. The cleanest October on record here was 2025 (median AQI 33, 0 days above 100) and the worst was 2024 (median 40, 1 day above 100, peak AQI 162).
- Good: 69.6%
- Moderate: 29.5%
- Unhealthy for Sensitive Groups: 0.5%
- Unhealthy or worse: 0.5%
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 is the air in Boston in October?
Good on a typical day: median AQI 42 across 2019–2025, with 1.0% of October days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓69.6% of October days were Good (AQI 0–50), 29.5% Moderate (51–100).
- ✓2 days of 217 reached AQI 101+; the October peak was 162.
- ✓Best October: 2025; worst October: 2024.
Frequently asked questions
What is the air quality like in Boston in October?▾
Across 2019–2025, the median daily AQI in Boston in October was 42 (Good). 69.6% of days were Good, 29.5% Moderate, and 1.0% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is October a good time for outdoor exercise in Boston?▾
A typical October day in Boston sits in the Good range (median AQI 42), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 100 of October days (1.0%) reached AQI 101+ in 2019–2025.
Which pollutant causes Boston's October air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 70.5% of October days in Boston. The highest October AQI recorded in 2019–2025 was 162 (Unhealthy), in 2024.
Boston October air quality, year by year
Boston October 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 | 31 | 45 | 0 | 59 | PM2.5 |
| 2020 | 31 | 46 | 0 | 65 | PM2.5 |
| 2021 | 31 | 42 | 0 | 55 | PM2.5 |
| 2022 | 31 | 51 | 0 | 74 | PM2.5 |
| 2023 | 31 | 33 | 1 | 102 | PM2.5 |
| 2024worst | 31 | 40 | 1 | 162 | O3 |
| 2025cleanest | 31 | 33 | 0 | 74 | O3 |
What October air means in Boston
A typical October day in Boston sits in the Good range (median AQI 42), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 100 of October days (1.0%) reached AQI 101+ in 2019–2025.
October's median AQI of 42 is below Boston's whole-year median of 48, making it one of the area's cleaner periods. Nationally, the median October AQI across every EPA metro area (102,872 metro-days, 2019–2025) is 38, so Boston runs above the national October norm; 1.0% of its October days topped AQI 100 versus 1.3% nationally (about the same).
October is part of Boston's fall season (September, October, November); the fall page pools all three months.
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 month 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.