| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 16°F | 34°F | 25°F | 6.6" |
| February | 16°F | 34°F | 25°F | 4.8" |
| March | 24°F | 41°F | 33°F | 6.1" |
| April | 35°F | 52°F | 43°F | 5.2" |
| May | 44°F | 61°F | 52°F | 6.0" |
| June | 52°F | 68°F | 60°F | 7.2" |
| July | 58°F | 75°F | 66°F | 8.7" |
| August | 57°F | 75°F | 65°F | 6.7" |
| September | 51°F | 69°F | 60°F | 7.8" |
| October | 41°F | 58°F | 50°F | 7.9" |
| November | 32°F | 49°F | 40°F | 8.2" |
| December | 22°F | 39°F | 30°F | 6.2" |
| Index | Belfast | Maine | National |
| Air quality index | 36 | 33 | 42 |
| Pollution index | 1,854,040 | 3,417,521 | 2,726,193 |
| Measurement | Total |
| Days measured | 213 |
| Days with good air quality | 204 |
| Days with moderate air quality | 9 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.004% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.005% |
| Lead | 0.010% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Bucksport, ME | 2,879 | 31 | 38.0% |
| Searsport, ME | 1,039 | 31 | 38.0% |
| Castine, ME | 813 | 36 | 28.0% |
| Camden, ME | 3,543 | 36 | 28.0% |
| Belfast, ME | 6,710 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Lake Hallie, WI | 6,710 | 34 | 32.0% |
| Avon, CO | 6,711 | 47 | 6.0% |
| Moapa Valley, NV | 6,708 | 54 | 8.0% |
| Lionville, PA | 6,707 | 42 | 16.0% |
| Scottsburg, IN | 6,715 | 35 | 30.0% |
| Belfast, ME | 6,710 | 36 | 28.0% |
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