| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 39°F | 30°F | 3.0" |
| February | 23°F | 40°F | 31°F | 2.6" |
| March | 30°F | 49°F | 39°F | 3.5" |
| April | 41°F | 62°F | 50°F | 4.2" |
| May | 50°F | 71°F | 60°F | 4.2" |
| June | 60°F | 79°F | 69°F | 5.1" |
| July | 66°F | 84°F | 74°F | 4.4" |
| August | 64°F | 82°F | 72°F | 4.2" |
| September | 57°F | 77°F | 66°F | 4.3" |
| October | 47°F | 65°F | 55°F | 5.1" |
| November | 37°F | 54°F | 45°F | 3.1" |
| December | 29°F | 44°F | 36°F | 4.5" |
| Index | Cos Cob | Connecticut | National |
| Air quality index | 43 | 43 | 42 |
| Pollution index | 16,950,700 | 8,629,883 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 262 |
| Days with moderate air quality | 82 |
| Days w/ poor A.Q. for sensitive groups | 18 |
| Days with unhealthy air quality | 3 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.140% |
| Carbon Tetrachloride | 0.070% |
| Lead | 0.080% |
| Mercury | 0.030% |
| City | Population | Air Quality Index | National Avg. |
| Cold Spring Harbor, NY | 2,864 | 43 | 14.0% |
| Cannondale, CT | 440 | 43 | 14.0% |
| Norwalk, CT | 88,755 | 43 | 14.0% |
| Westport, CT | 27,511 | 43 | 14.0% |
| Bedford Hills, NY | 2,892 | 43 | 14.0% |
| Cos Cob, CT | 7,065 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| Hewlett, NY | 7,064 | 51 | 2.0% |
| Delphos, OH | 7,066 | 39 | 22.0% |
| Hudson Falls, NY | 7,067 | 35 | 30.0% |
| Saint-Apollinaire, QC | 7,067 | n/a | |
| Clarkston Heights-Vineland, WA | 7,062 | 29 | 42.0% |
| Cos Cob, CT | 7,065 | 43 | 14.0% |
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