Bad Air Days in Hampden County, Massachusetts: 3 a Year

3 bad air days a year

About the middle of monitored US counties. Ranked 398 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (21% particle days).

Which months to watch

Most bad days here fall in June and May and July and August. Averaged over 2016 to 2025.

What actually helps here

Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
On the odd bad day, check AirNow and keep windows shut.

Better or worse than it was

In 2000 to 2009 this county averaged 21 bad days a year; in 2016 to 2025, 3. The air has improved. The worst recent year was 2016, with 6 bad days on 366 monitored days.

Date	AQI	Main pollutant
2016-05-26	161	Ozone
2023-06-07	153	PM2.5
2023-06-08	153	PM2.5
2023-07-01	150	Ozone
2023-06-06	141	PM2.5

An ordinary day in Hampden

Across 3,652 monitored days from 2016 to 2025, the air in Hampden County rated Good on 70% of them, close to the 72% typical of monitored counties, and Moderate on 29%. The median day sat at AQI 42; one day in ten went above 61.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)52%1,905 days
ozone46%1,684 days
nitrogen dioxide2%63 days

Hampden County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	281	79	5	0	39	124
2024	366	290	74	2	0	37	119
2023	365	220	139	6	2	46	153
2022	365	262	102	1	0	42	115
2021	365	215	148	2	0	46	116
2020	366	249	117	0	0	44	99
2019	364	260	104	0	0	43	93
2018	365	248	115	2	0	41	126
2017	365	270	91	4	0	42	112
2016	366	276	84	6	1	41	161
2015	365	231	131	3	0	43	147
2014	365	213	152	0	0	46	100
2013	365	224	135	6	0	45	140
2012	366	179	176	11	0	51	147
2011	365	176	176	13	2	52	162
2010	365	187	168	10	1	49	164

*2025 may be a partial year in EPA's file.

Massachusetts compared

How this is counted

A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.