Bad Air Days in Merrimack County, New Hampshire: under 1 a Year
under 1 bad air days a year
Rare: among the cleanest-air counties EPA monitors. Ranked 932 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (0% particle days).
The bad-air season here
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in June. Averaged over 2016 to 2025.
What to buy, and what not to
- 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 worst days on file
In 2000 to 2009 this county averaged 7 bad days a year; in 2016 to 2025, under 1. The air has improved. The worst recent year was 2021, with 1 bad day on 214 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2021-06-06 | 101 | Ozone |
| 2023-04-14 | 100 | Ozone |
| 2023-07-13 | 93 | Ozone |
| 2017-04-10 | 90 | Ozone |
| 2017-04-11 | 90 | Ozone |
An ordinary day in Merrimack
Across 2,423 monitored days from 2016 to 2025, the air in Merrimack County rated Good on 96% of them, more often than the 72% typical of monitored counties, and Moderate on 4%. The median day sat at AQI 35; one day in ten went above 46.
The pollutant setting the AQI on an ordinary day here:
- ozone100%2,423 days
Year by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 212 | 205 | 7 | 0 | 0 | 37 | 90 |
| 2024 | 214 | 205 | 9 | 0 | 0 | 37 | 74 |
| 2023 | 213 | 197 | 16 | 0 | 0 | 39 | 100 |
| 2022 | 212 | 205 | 7 | 0 | 0 | 36 | 84 |
| 2021 | 214 | 200 | 13 | 1 | 0 | 36 | 101 |
| 2020 | 213 | 209 | 4 | 0 | 0 | 38 | 74 |
| 2019 | 210 | 206 | 4 | 0 | 0 | 36 | 61 |
| 2018 | 213 | 203 | 10 | 0 | 0 | 38 | 87 |
| 2017 | 364 | 352 | 12 | 0 | 0 | 32 | 90 |
| 2016 | 358 | 344 | 14 | 0 | 0 | 31 | 84 |
| 2015 | 362 | 354 | 7 | 1 | 0 | 33 | 105 |
| 2014 | 297 | 259 | 37 | 1 | 0 | 33 | 101 |
| 2013 | 244 | 193 | 51 | 0 | 0 | 37 | 97 |
| 2012 | 242 | 178 | 63 | 1 | 0 | 42 | 101 |
| 2011 | 242 | 184 | 58 | 0 | 0 | 38 | 93 |
| 2010 | 238 | 173 | 62 | 3 | 0 | 40 | 126 |
*2025 may be a partial year in EPA's file.
Nearby counties on file
- Coos County2/yr
- Rockingham County2/yr
- Hillsborough County1/yr
- Cheshire Countyunder 1/yr
- Grafton Countyunder 1/yr
- Belknap Countyunder 1/yr
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.