Middlesex County, Massachusetts

AQI 41 · Good

YearMonth

41

Median AQI

58

90th Percentile

105

Max AQI

243

Days with Data

Ranked #10 of 13 counties in Massachusetts (by median AQI, lower is better)

Monthly Median AQI — 2025

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AQI Category Breakdown

Adjacent Counties

Essex County Norfolk County Suffolk County Worcester County Hillsborough County, New Hampshire

External Links

Middlesex County, Massachusetts on Wikipedia