# Massachusetts air quality today — live AQI by metro > Source: https://breathecheck.com/air-quality/us/massachusetts/ > Live AQI for 2 Massachusetts metros, updated hourly from EPA AirNow. Where the state's air is worst right now, and how far apart its cities are. # Massachusetts air quality today Updated 14 Sep 2026, 22:12 UTC · LIVE 2 metros tracked Across the 2 Massachusetts metros BreatheCheck measures, air is worst right now in Worcester at AQI 25 (Good) and cleanest in Boston at AQI 24 . ## Which Massachusetts city has the worst air quality right now? | # | Metro | AQI | UV now | Dominant | | 1 | Worcester no page yet | 25 Good | 0.2 | O3 | | 2 | Boston | 24 Good | 0.2 | O3 | ## What is the UV index in Massachusetts today? The strongest UV in Massachusetts today is 5.5 (High) in Boston, arriving around 12pm local time. The mildest of the 2 metros we model here peaks at 5.5 in Worcester. UV is modelled, not measured — unlike the AQI above it, which comes off an instrument. Hour by hour in Boston → ## Alerts that name one corner, not the state Read a season of MassDEP air quality alerts and the geography shows up in the warnings themselves: some are issued for five southeastern counties alone — Barnstable, Bristol, Dukes, Nantucket and Plymouth — with the rest of the state left out of them. That corner sits at the downwind end of the coastal plume running up from the New York and Connecticut corridor, and ozone has hours over open water to keep forming before it makes landfall there. Metro Boston’s traffic adds to what moves downwind, but the highest readings often land well past the city that produced part of them. Winter inverts the map. In the valleys of western Massachusetts, wood stove smoke is held under inversions through the cold months and pushes fine particle concentrations up locally, in towns carrying a small fraction of the eastern population. Two pollutants, two halves of the state, six months apart, sharing one index and one state average that describes neither. MassDEP’s Air Assessment Branch runs the regulatory monitoring network and has added roughly 200 small area monitors for fine particles and ozone, placed in rural communities and environmental justice areas. Those readings appear on AirNow’s Fire and Smoke Map alongside personal and community-owned sensors; the regulatory data and the daily forecast publish through MassAir Online. Where a Massachusetts metro in the table above has no page of ours, that is a gap in what we have built, not a reading we took. ## Where do these Massachusetts readings come from? 2 of the 2 metros here report from a named regulatory monitor — Boston Metro, Worcester. The dominant pollutant across Massachusetts today is O3 . We track 2 metropolitan areas in Massachusetts, not the whole state, and 1 of them has a page of its own. There is no state-wide average here on purpose: averaging 2 metros into one figure would invent a value for all the ground between them. How we measure, and what we refuse to estimate → ## Neighbouring states Smoke and inversions do not stop at a state line, so when Massachusetts looks wrong the answer is often next door. ## Related Updated 14 Sep 2026, 22:12 UTC