| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 19°F | 36°F | 27°F | 5.3" |
| February | 19°F | 37°F | 27°F | 6.2" |
| March | 27°F | 45°F | 35°F | 7.3" |
| April | 37°F | 58°F | 47°F | 7.5" |
| May | 47°F | 68°F | 57°F | 7.1" |
| June | 56°F | 76°F | 65°F | 8.3" |
| July | 63°F | 83°F | 72°F | 7.9" |
| August | 60°F | 81°F | 70°F | 8.4" |
| September | 54°F | 74°F | 63°F | 8.5" |
| October | 43°F | 63°F | 52°F | 8.2" |
| November | 33°F | 52°F | 42°F | 6.9" |
| December | 24°F | 41°F | 32°F | 6.3" |
| Index | Portsmouth | New Hampshire | National |
| Air quality index | 37 | 34 | 42 |
| Pollution index | 91,790 | 3,959,618 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 353 |
| Days with moderate air quality | 12 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.002% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.001% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Berwick, ME | 1,985 | 27 | 46.0% |
| Hampton Beach, NH | 2,485 | 37 | 26.0% |
| Kittery, ME | 5,297 | 37 | 26.0% |
| Durham, NH | 12,016 | 37 | 26.0% |
| South Eliot, ME | 3,047 | 37 | 26.0% |
| Portsmouth, NH | 21,418 | 37 | 26.0% |
| City | Population | Air Quality Index | National Avg. |
| Mukilteo, WA | 21,414 | 45 | 10.0% |
| North Bellmore, NY | 21,422 | 51 | 2.0% |
| Duarte, CA | 21,399 | 72 | 44.0% |
| Bear, DE | 21,397 | 42 | 16.0% |
| Ensley, FL | 21,397 | 41 | 18.0% |
| Portsmouth, NH | 21,418 | 37 | 26.0% |
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