Boston Air Quality in August
Across 2019–2025, Boston's August air quality had a median AQI of 52 (Moderate) over 217 monitored days in the Boston-Cambridge-Newton, MA-NH area. 2.3% of August days (5 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 61.3% of days. The cleanest August on record here was 2023 (median AQI 49, 0 days above 100) and the worst was 2022 (median 51, 2 days above 100, peak AQI 113).
- Good: 47.0%
- Moderate: 50.7%
- Unhealthy for Sensitive Groups: 2.3%
- 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 is the air in Boston in August?
Moderate on a typical day: median AQI 52 across 2019–2025, with 2.3% of August days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓47.0% of August days were Good (AQI 0–50), 50.7% Moderate (51–100).
- ✓5 days of 217 reached AQI 101+; the August peak was 150.
- ✓Best August: 2023; worst August: 2022.
Frequently asked questions
What is the air quality like in Boston in August?▾
Across 2019–2025, the median daily AQI in Boston in August was 52 (Moderate). 47.0% of days were Good, 50.7% Moderate, and 2.3% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is August a good time for outdoor exercise in Boston?▾
A typical August 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 43 of August days (2.3%) 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 August air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 61.3% of August days in Boston. The highest August AQI recorded in 2019–2025 was 150 (Unhealthy for Sensitive Groups), in 2022.
Boston August air quality, year by year
Boston August 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 | 52 | 0 | 100 | PM2.5 |
| 2020 | 31 | 54 | 0 | 97 | PM2.5 |
| 2021 | 31 | 53 | 1 | 122 | PM2.5 |
| 2022worst | 31 | 51 | 2 | 113 | O3 |
| 2023cleanest | 31 | 49 | 0 | 66 | PM2.5 |
| 2024 | 31 | 52 | 0 | 87 | PM2.5 |
| 2025 | 31 | 47 | 2 | 150 | O3 |
What August air means in Boston
A typical August 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 43 of August days (2.3%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
August'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 August AQI across every EPA metro area (104,152 metro-days, 2019–2025) is 45, so Boston runs above the national August norm; 2.3% of its August days topped AQI 100 versus 3.5% nationally (below average).
August is part of Boston's summer season (June, July, August); the summer 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.