| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 21°F | 39°F | 30°F | 2.9" |
| February | 21°F | 40°F | 31°F | 3.1" |
| March | 29°F | 49°F | 39°F | 3.5" |
| April | 40°F | 63°F | 51°F | 4.2" |
| May | 50°F | 73°F | 61°F | 3.8" |
| June | 60°F | 81°F | 70°F | 5.1" |
| July | 66°F | 86°F | 76°F | 4.5" |
| August | 64°F | 84°F | 73°F | 4.1" |
| September | 57°F | 78°F | 67°F | 3.5" |
| October | 46°F | 66°F | 55°F | 5.2" |
| November | 35°F | 54°F | 44°F | 3.3" |
| December | 27°F | 43°F | 35°F | 4.2" |
| Index | Portland | Connecticut | National |
| Air quality index | 41 | 43 | 42 |
| Pollution index | 4,117,250 | 8,629,883 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 291 |
| Days with moderate air quality | 66 |
| Days w/ poor A.Q. for sensitive groups | 7 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.010% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Colchester, CT | 5,147 | 33 | 34.0% |
| Moodus, CT | 1,802 | 37 | 26.0% |
| Chester Center, CT | 1,731 | 37 | 26.0% |
| Manchester, CT | 35,946 | 41 | 18.0% |
| New Britain, CT | 72,543 | 41 | 18.0% |
| Portland, CT | 5,937 | 41 | 18.0% |
| City | Population | Air Quality Index | National Avg. |
| Hilmar-Irwin, CA | 5,937 | 49 | 2.0% |
| Pevely, MO | 5,937 | 54 | 8.0% |
| Annapolis, Subd. A, NS | 5,937 | n/a | |
| Brownfields, LA | 5,936 | 45 | 10.0% |
| Lake Mills, WI | 5,936 | 37 | 26.0% |
| Portland, CT | 5,937 | 41 | 18.0% |
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