Bad Air Days in Rockingham County, New Hampshire: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 556 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (12% particle days).

The bad-air season here

Most bad days here fall in July and June 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.

The record for Rockingham

In 2000 to 2009 this county averaged 10 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2021, with 4 bad days on 365 monitored days.

Date	AQI	Main pollutant
2025-08-12	150	Ozone
2021-07-26	147	PM2.5
2016-07-06	122	Ozone
2021-08-26	122	Ozone
2022-07-20	122	Ozone

An ordinary day in Rockingham

Across 3,653 monitored days from 2016 to 2025, the air in Rockingham County rated Good on 82% of them, more often than the 72% typical of monitored counties, and Moderate on 18%. The median day sat at AQI 40; one day in ten went above 56.

The pollutant setting the AQI on an ordinary day here:

ozone67%2,433 days
fine particles (PM2.5)33%1,219 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	309	54	2	0	38	150
2024	366	306	59	1	0	38	122
2023	365	276	89	0	0	40	100
2022	365	292	71	2	0	40	122
2021	365	285	76	4	0	40	147
2020	366	296	70	0	0	41	90
2019	365	319	45	1	0	39	112
2018	365	309	53	3	0	39	115
2017	365	310	53	2	0	39	112
2016	366	289	75	2	0	41	122
2015	365	202	161	2	0	47	126
2014	365	157	204	4	0	52	112
2013	365	190	172	3	0	50	119
2012	366	255	106	5	0	43	143
2011	365	219	143	3	1	46	151
2010	363	281	78	4	1	39	155

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

New Hampshire 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.