Massachusetts air quality today

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.