SmogRank / World / United States / Massachusetts / May 2025

Most polluted cities in Massachusetts, United States, May 2025

16 cities in Massachusetts, United States ranked by their average PM2.5 over the 31 days. Worst: Boston at 5.4 µg/m³, #2,110 of 2,771 cities in the world. Cleanest: Ware at 3.6. A city needs measurements on 70% of the days to be ranked.

Ranked by unhealthy days: the share of each city's measured days with a daily mean over 35.4 µg/m³ (US AQI 101+), Unhealthy for Sensitive Groups or worse on the US EPA's scale. Ties go to the higher average.

← Boston 0% 0.75%0
Every city in Massachusetts, United States ranked for May 2025, one column each, ranked by unhealthy days: height is the share of its measured days that were unhealthy, colour its average. Point at it to read a city; tap to open it.
Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales

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SmogRank, most polluted cities in Massachusetts, United States, PM2.5, May 2025, smogrank.com/us/region/massachusetts/history/2025-05 (accessed 6 Oct 2026).

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You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.