Boston Air Quality in Summer
Across 2019–2025, Boston's summer (June–August) air quality had a median AQI of 52 (Moderate) over 644 monitored days in the Boston-Cambridge-Newton, MA-NH area. 3.5% of summer days (22 of 644) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 61.2% of days. The cleanest summer on record here was 2020 (median AQI 53, 0 days above 100) and the worst was 2022 (median 51, 6 days above 100, peak AQI 122).
- Good: 42.4%
- Moderate: 54.2%
- Unhealthy for Sensitive Groups: 3.3%
- Unhealthy or worse: 0.2%
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
As an Amazon Associate, we earn from qualifying purchases.
How is the air in Boston in summer?
Moderate on a typical day: median AQI 52 across 2019–2025, with 3.5% of summer days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓42.4% of summer days were Good (AQI 0–50), 54.2% Moderate (51–100).
- ✓22 days of 644 reached AQI 101+; the summer peak was 153.
- ✓Cleanest month: August; worst month: July.
Frequently asked questions
What is the air quality like in Boston in summer?▾
Across 2019–2025, the median daily AQI in Boston in summer was 52 (Moderate). 42.4% of days were Good, 54.2% Moderate, and 3.5% reached Unhealthy for Sensitive Groups or worse, based on 644 monitored days in EPA's Air Quality System.
Is summer a good time for outdoor exercise in Boston?▾
A typical summer day in Boston is Moderate (median AQI 52): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 29 of summer days (3.5%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Boston's summer air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 61.2% of summer days in Boston. The highest summer AQI recorded in 2019–2025 was 153 (Unhealthy), in 2022.
Boston summer air quality, year by year
Boston summer 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 | 92 | 52 | 1 | 122 | PM2.5 |
| 2020cleanest | 92 | 53 | 0 | 97 | PM2.5 |
| 2021 | 92 | 53 | 5 | 153 | PM2.5 |
| 2022worst | 92 | 51 | 6 | 122 | PM2.5 |
| 2023 | 92 | 53 | 4 | 136 | PM2.5 |
| 2024 | 92 | 52 | 1 | 122 | O3 |
| 2025 | 92 | 51 | 5 | 150 | O3 |
What summer air means in Boston
A typical summer day in Boston is Moderate (median AQI 52): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 29 of summer days (3.5%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Summer's median AQI of 52 is above Boston's whole-year median of 48, making it one of the area's dirtier periods. Nationally, the median Summer AQI across every EPA metro area (308,645 metro-days, 2019–2025) is 46, so Boston runs above the national Summer norm; 3.5% of its Summer days topped AQI 100 versus 3.6% nationally (about the same).
Within the season, August is the cleanest month (median AQI 52, 2.3% of days above 100) and July the worst (median 54, 4.2% above 100).
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 season 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.