Bad Air Days in Hampshire County, Massachusetts: 2 a Year

2 bad air days a year

About the middle of monitored US counties. Ranked 488 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (33% particle days).

The bad-air season here

Most bad days here fall in June and May and July. 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.

The record for Hampshire

In 2000 to 2009 this county averaged 16 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2023, with 6 bad days on 365 monitored days.

Date	AQI	Main pollutant
2016-05-26	159	Ozone
2023-07-01	138	PM2.5
2023-06-08	132	PM2.5
2023-06-06	128	PM2.5
2017-05-17	122	Ozone

The air on a normal day

Across 3,630 monitored days from 2016 to 2025, the air in Hampshire County rated Good on 82% of them, more often than the 72% typical of monitored counties, and Moderate on 17%. The median day sat at AQI 38; one day in ten went above 54.

The pollutant setting the AQI on an ordinary day here:

ozone66%2,391 days
fine particles (PM2.5)33%1,216 days
nitrogen dioxide1%20 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	312	49	4	0	36	117
2024	366	324	40	2	0	35	112
2023	365	292	67	6	0	38	138
2022	365	267	98	0	0	42	97
2021	352	307	45	0	0	35	96
2020	366	300	66	0	0	39	84
2019	364	296	68	0	0	41	93
2018	363	282	79	2	0	40	122
2017	365	310	52	3	0	38	122
2016	359	302	53	4	1	38	159
2015	361	295	62	4	0	37	108
2014	365	228	137	0	0	44	100
2013	365	230	133	2	0	44	115
2012	366	281	74	11	0	38	140
2011	365	271	91	3	0	41	147
2010	365	273	83	9	1	39	159

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

Elsewhere in Massachusetts

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.