| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 15°F | 36°F | 25°F | 3.2" |
| February | 15°F | 37°F | 26°F | 4.2" |
| March | 24°F | 44°F | 34°F | 4.0" |
| April | 34°F | 57°F | 45°F | 5.0" |
| May | 44°F | 67°F | 55°F | 4.5" |
| June | 53°F | 75°F | 63°F | 5.8" |
| July | 60°F | 82°F | 70°F | 4.3" |
| August | 58°F | 80°F | 69°F | 4.4" |
| September | 51°F | 74°F | 62°F | 4.1" |
| October | 41°F | 62°F | 51°F | 6.9" |
| November | 31°F | 52°F | 41°F | 4.4" |
| December | 21°F | 40°F | 30°F | 5.3" |
| Index | Riverton | Portland | Maine |
| Air quality index | 40 | 40 | 33 |
| Pollution index | 2,043,700 | 2,043,700 | 3,417,521 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 308 |
| Days with moderate air quality | 56 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.003% |
| Lead | 0.030% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Gray, ME | 747 | 31 | 38.0% |
| Biddeford, ME | 21,502 | 40 | 20.0% |
| Saco, ME | 19,716 | 40 | 20.0% |
| North Windham, ME | 5,651 | 40 | 20.0% |
| Falmouth, ME | 1,877 | 40 | 20.0% |
| Portland, ME | 66,706 | 40 | 20.0% |
| City | Population | Air Quality Index | National Avg. |
| West Des Moines, IA | 66,724 | 39 | 22.0% |
| Redondo Beach, CA | 66,663 | 72 | 44.0% |
| Yuba City, CA | 66,660 | 44 | 12.0% |
| Oshkosh, WI | 66,753 | 36 | 28.0% |
| Kenner, LA | 66,759 | 45 | 10.0% |
| Portland, ME | 66,706 | 40 | 20.0% |
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