Air quality in New Hampshire
EPA monitors report from 7 of New Hampshire’s 10 counties. That is the honest limit of this page: the other 3 are not measured, not clean. In 2025 the most affected monitored county was Coos County, with 4 days above the moderate category.
7
Counties with monitors
3
Counties without
15
Days above moderate, 2025
Summed across monitored counties
10.5%
Adults with asthma
Population-weighted county estimate
County by county
Monitored New Hampshire counties
GoodModerateUnhealthy for sensitive groupsUnhealthyVery unhealthyHazardous
| County | 90th %ile AQI | Above moderate | Max AQI | 2025 days by category |
|---|---|---|---|---|
| Coos County | 61 | 4 | 119 | |
| Hillsborough County | 55 | 4 | 123 | |
| Grafton County | 54 | 3 | 113 | |
| Cheshire County | 57 | 2 | 115 | |
| Rockingham County | 54 | 2 | 150 | |
| Belknap County | 51 | 0 | 92 | |
| Merrimack County | 46 | 0 | 90 |
EPA Air Quality System annual summaries by county, 2025. The 90th percentile AQI describes a day worse than nine out of ten, which is a steadier measure than the annual maximum a single wildfire can set.
Not measured
3 counties without a monitor
No EPA monitor reported from these counties, so there is no air quality record to publish. Their radon zone is known, and radon is measured in the building rather than the air outside it.
Other states
Air quality elsewhere
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