Nearly two million Massachusetts residents live in counties with failing or near-failing air quality. That is one of the findings of a new report on ozone levels by the American Lung Association that assigns letter grades to counties. The report released early Wednesday found that of the 12 Massachusetts counties with air pollution monitors, three — Barnstable, Hampden, and Norfolk — improved one letter grade for ozone pollution. Essex county jumped two grades from an F to a C. Four counties — Hampshire, Worcester, Bristol, and Dukes — received an F.

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