Right now: Boston is at 24, good.
Is the air safe to breathe in Boston today?
In Boston, BreatheCheck reads 24 as Go. The cutoffs: go below 101, keep it short and easy from 101 to 150, move it indoors above 150. These are our own thresholds, drawn on the EPA bands — EPA itself classifies 101–150 as Unhealthy for Sensitive Groups and does not tell you how long to stay out.
Go AQI 0–100
Normal outdoor plans. No change needed.
Short & unloaded AQI 101–150
A 20-minute dog walk, not a 2.5-hour run. Keep it brief and easy.
Don’t go AQI 151+
Move it indoors. Above 200 that becomes everyone, not just sensitive groups.
Above 200 this stops being a personal call: everyone indoors.
Duration and intensity are two separate dials
| Under 20 min | 20–60 min | Over an hour | |
|---|---|---|---|
| Easy | Go | Go | Go |
| Moderate | Go | Go | Go |
| Hard | Go | Go | Go |
Go Every combination lands the same way at this reading — a hard hour is no different from an easy twenty minutes. The two dials separate above 80.
Where people actually draw the line
All the thresholds people reported, and who reported them
- 60 Asthmatic runnerone runner’s own 156-run log
- 75–100 Daycare / schoolparents and staff in one r/toddlers thread, Aug 2025 — not a published rule
- 100 Parentcommunity-reported, escalating at 150 and 200
- 110 Runnercommunity-reported
If you’re staying in, filter the room you’re actually in
Ozone made here usually peaks somewhere else
Ozone is not emitted by anything. It is assembled in sunlight out of nitrogen oxides and volatile organic compounds, and fresh vehicle exhaust destroys it on contact, so the highest readings turn up well downwind of the traffic that supplied the ingredients rather than in the middle of it.
Which direction downwind lies matters more here than it would inland. Boston’s worst ozone comes with flow arriving off the continent, and downwind of the city on those days is Massachusetts Bay, the South Shore and the arm of the Cape — water and thinly built coastline rather than another metro. The reaction finishes out there, over places that put almost none of the ingredients in.
The sea breeze complicates that rather than resolving it. The Boston Basin is flat through the middle and ringed by low hills, the Middlesex Fells around to the Blue Hills, and on summer afternoons a breeze off Massachusetts Bay can turn air that had already blown out over the water and push it back across the city. An onshore wind here is not automatically a clean one. Some of what it delivers left the city a few hours earlier.
Where this number sits
Of the 121 US metros reporting to us right now, Boston is number 108 and number 2 of the 2 we track in Massachusetts. The pollutant driving it today is O3.
Nearby metros we also measure, and what they read at the same hour:
- Nashua, NH — 35 miles away, AQI 28
- Worcester, MA — 38 miles away, AQI 25
- Providence, RI — 41 miles away, AQI 29
- Manchester, NH — 48 miles away, AQI 31
Where this reading comes from
AirNow’s Boston Metro reporting area, about 4.2 miles from the metro centre.
What has air quality in Boston actually been?
0 of the 30 days we have recorded so far went above AQI 100.
| Date | Daily max AQI | EPA band | Hours read |
|---|---|---|---|
| 35 | Good | 22 | |
| 52 | Moderate | 23 | |
| 53 | Moderate | 23 | |
| 35 | Good | 23 | |
| 46 | Good | 23 | |
| 52 | Moderate | 23 | |
| 43 | Good | 23 | |
| 38 | Good | 23 | |
| 24 | Good | 23 | |
| 49 | Good | 23 | |
| 52 | Moderate | 23 | |
| 29 | Good | 24 | |
| 29 | Good | 23 | |
| 36 | Good | 23 | |
| 43 | Good | 23 | |
| 42 | Good | 23 | |
| 48 | Good | 23 | |
| 46 | Good | 22 | |
| 43 | Good | 23 | |
| 33 | Good | 23 | |
| 54 | Moderate | 23 | |
| 55 | Moderate | 24 | |
| 43 | Good | 23 | |
| 52 | Moderate | 23 | |
| 52 | Moderate | 23 | |
| 96 | Moderate | 23 | |
| 48 | Good | 23 | |
| 43 | Good | 22 | |
| 34 | Good | 26 | |
| 38 | Good | 7 — partial day |
Questions about Boston
What is the air quality in Boston right now?
Which monitor does this number come from?
How does Boston compare with metros nearby?
Does this include pollen?
Put this number in context
Updated