Air quality · ZIP 02139
Air quality in Cambridge, MA
In 2025, Middlesex County, Massachusetts — the county ZIP 02139 is in — had a median daily AQI of 38, which EPA rates Good. Of 365 days with a reading, 299 were Good, 65 Moderate and 1 Unhealthy for Sensitive Groups. This is EPA's annual county summary, not today's air.
Middlesex County, Massachusetts · 2025 annual summary
Median AQI 38 — Good
Air quality is satisfactory, and air pollution poses little or no risk.
- Good days
- 299
- Moderate days
- 65
- Unhealthy for sensitive groups
- 1
- Unhealthy+ days
- 0
- Max AQI
- 105
- 90th percentile AQI
- 56
This is a county-level ANNUAL SUMMARY for 2025, not a live current reading. For today's air quality, check a real-time monitor at airnow.gov. Categories follow EPA's official AQI breakpoints.
Next step for your own home
What this page shows
The 2025 annual EPA Air Quality System summary for this ZIP's county — shown above.
Source & refresh
EPA Air Quality System (AQS), annual county summary. The figures are EPA's 2025 annual county summary. EPA publishes one summary a year, so this is not today's air. Primary source →
Limitations specific to this source
This is a county-level ANNUAL SUMMARY, not a live current reading and not an address-level measurement — for today's AQI, EPA's real-time AirNow feed is the correct source (not yet federated here). Not every county operates an EPA monitor; absence of data for a ZIP's county means no 2025 EPA reading exists, not that air is good.
Massachusetts context
Lead pipes, coastal flood, older housing
Massachusetts has dense lead-service-line obligations under LCRR in Boston, Lowell, Worcester, Springfield. Coastal AE/VE zones along the South Shore + Cape. Older housing stock means lead-paint risk overlaps with LSL risk.
See Massachusetts state page for the full state-level rollup across all 12 dimensions.
Read more on air quality
Editorial deep-dives explaining the source data, its limits, and how to read it.
EPA AQI categories explained — what 0–50 Good through 301–500 Hazardous mean
Plain-English guide to the six EPA Air Quality Index categories: 0–50 Good, 51–100 Moderate, 101–150 Unhealthy for Sensitive Groups, 151–200 Unhealthy, 201–300 Very Unhealthy, 301–500 Hazardous — what each level means and who is at risk.
AQI explained — what 50, 100, 150 actually mean for your lungs
Plain-English guide to the EPA Air Quality Index (AQI) and the 6 categories from Good to Hazardous. When to take precautions and which pollutants matter.
Wildfire Hazard Potential — what the USFS scale means and how to defend your home
Plain-English guide to the USDA Forest Service's Wildfire Hazard Potential 1–5 scale, how to read your community's risk, and concrete home-defense measures.
AirNow + wildfire smoke — when AQI is a real-time tool
How EPA AirNow handles real-time wildfire smoke, what the colors mean during fire season, and where AirNow leaves gaps you should know about.
The other dimensions for ZIP 02139
Air quality is one of twelve public-records dimensions zipradar indexes per address. See the ZIP 02139 index for the other eleven — each with its own regulator, source and link:
All dimensions for Cambridge, MA →Frequently asked questions
What is the air quality for ZIP 02139?
Middlesex County, Massachusetts (which covers ZIP 02139) had a 2025 median AQI of 38 — Good, per EPA's Air Quality System. Over the year: 299 Good days, 65 Moderate, 1 Unhealthy for Sensitive Groups. This is a county-level ANNUAL SUMMARY for 2025, not a live current reading. For today's air quality, check a real-time monitor at airnow.gov. Categories follow EPA's official AQI breakpoints.
Where does the air quality data come from?
Source: EPA Air Quality System (AQS), annual county summary. The figures are EPA's 2025 annual county summary. EPA publishes one summary a year, so this is not today's air. The original is at https://aqs.epa.gov/aqsweb/airdata/download_files.html.
What are the limitations of air quality data?
This is a county-level ANNUAL SUMMARY, not a live current reading and not an address-level measurement — for today's AQI, EPA's real-time AirNow feed is the correct source (not yet federated here). Not every county operates an EPA monitor; absence of data for a ZIP's county means no 2025 EPA reading exists, not that air is good.
Is ZIP 02139 (Cambridge) data current?
zipradar last checked this page against the source on 2026-09-24. The figures are EPA's 2025 annual county summary. EPA publishes one summary a year, so this is not today's air. The ZIP 02139 overview at /zip/02139/ lists the other topics zipradar covers for this ZIP.