Bad Air Days in Cheshire County, New Hampshire: under 1 a Year

under 1 bad air day a year

Rare: among the cleanest-air counties EPA monitors. Ranked 789 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (83% particle days).

When the bad days come in Cheshire

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

Is a purifier worth it 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 6 bad days a year; in 2016 to 2025, under 1. The air has improved. The worst recent year was 2023, with 2 bad days on 363 monitored days.

Date	AQI	Main pollutant
2021-07-26	127	PM2.5
2023-07-01	125	PM2.5
2025-07-26	115	PM2.5
2023-07-17	112	PM2.5
2025-08-05	109	PM2.5

Most days, not the worst ones

Across 3,649 monitored days from 2016 to 2025, the air in Cheshire County rated Good on 80% of them, more often than the 72% typical of monitored counties, and Moderate on 20%. The median day sat at AQI 37; one day in ten went above 56.

The pollutant setting the AQI on an ordinary day here:

ozone58%2,105 days
fine particles (PM2.5)42%1,544 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	288	75	2	0	37	115
2024	366	302	64	0	0	36	93
2023	363	253	108	2	0	41	125
2022	365	304	61	0	0	37	84
2021	364	263	100	1	0	40	127
2020	366	299	67	0	0	37	78
2019	365	331	34	0	0	35	82
2018	365	300	65	0	0	36	86
2017	364	298	66	0	0	37	93
2016	366	290	75	1	0	37	105
2015	365	224	140	1	1	44	155
2014	365	207	157	1	0	45	115
2013	365	241	121	3	0	43	108
2012	366	259	105	2	0	40	112
2011	365	209	152	4	0	45	134
2010	365	236	128	1	0	42	106

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

Nearby counties on file

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.