Air Quality in Massachusetts

Massachusetts has 13 counties with EPA air quality monitoring. Air quality is generally improving across the state, with an average of 312 "Good" days per county per year. The best air quality is in Hampshire (median AQI 35) and the most polluted is Norfolk (median AQI 39).

County	Median AQI	Max AQI	Good Days	Unhealthy Days	Trend	Top Pollutant
Barnstable	36	101	333	1	→ stable	Ozone
Berkshire	38	97	300	0	→ stable	Ozone
Bristol	38	108	322	2	→ stable	Ozone
Dukes	37	108	331	1	→ stable	Ozone
Essex	37	1513	300	4	→ stable	Ozone
Franklin	36	94	296	0	→ stable	Ozone
Hampden	37	119	290	2	→ stable	Ozone
Hampshire	35	112	324	2	→ stable	Ozone
Middlesex	37	93	314	0	→ stable	Ozone
Norfolk	39	90	319	0	→ stable	Ozone
Plymouth	37	97	319	0	→ stable	Ozone
Suffolk	36	78	291	0	↓ improving	PM2.5
Worcester	37	90	321	0	→ stable	Ozone