Boston Air Quality in July
Across 2019–2025, Boston's July air quality had a median AQI of 54 (Moderate) over 217 monitored days in the Boston-Cambridge-Newton, MA-NH area. 4.2% of July days (9 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 65.9% of days. The cleanest July on record here was 2020 (median AQI 53, 0 days above 100) and the worst was 2022 (median 55, 4 days above 100, peak AQI 122).
- Good: 31.3%
- Moderate: 64.5%
- Unhealthy for Sensitive Groups: 3.7%
- 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 July?
Moderate on a typical day: median AQI 54 across 2019–2025, with 4.2% of July days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓31.3% of July days were Good (AQI 0–50), 64.5% Moderate (51–100).
- ✓9 days of 217 reached AQI 101+; the July peak was 153.
- ✓Best July: 2020; worst July: 2022.
Frequently asked questions
What is the air quality like in Boston in July?▾
Across 2019–2025, the median daily AQI in Boston in July was 54 (Moderate). 31.3% of days were Good, 64.5% Moderate, and 4.2% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is July a good time for outdoor exercise in Boston?▾
A typical July day in Boston is Moderate (median AQI 54): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 24 of July days (4.2%) 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 July air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 65.9% of July days in Boston. The highest July AQI recorded in 2019–2025 was 153 (Unhealthy), in 2022.
Boston July air quality, year by year
Boston July 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 | 54 | 1 | 122 | PM2.5 |
| 2020cleanest | 31 | 53 | 0 | 90 | PM2.5 |
| 2021 | 31 | 54 | 2 | 153 | PM2.5 |
| 2022worst | 31 | 55 | 4 | 122 | PM2.5 |
| 2023 | 31 | 54 | 1 | 114 | PM2.5 |
| 2024 | 31 | 54 | 0 | 97 | O3 |
| 2025 | 31 | 52 | 1 | 106 | O3 |
What July air means in Boston
A typical July day in Boston is Moderate (median AQI 54): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 24 of July days (4.2%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
July's median AQI of 54 is above Boston's whole-year median of 48, making it one of the area's dirtier periods. Nationally, the median July AQI across every EPA metro area (103,858 metro-days, 2019–2025) is 47, so Boston runs above the national July norm; 4.2% of its July days topped AQI 100 versus 3.6% nationally (about the same).
July 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.