| 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 | Norwalk | 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. |
| Glenville, CT | 2,976 | 43 | 14.0% |
| Darien, CT | 21,519 | 43 | 14.0% |
| Ridgefield, CT | 7,228 | 43 | 14.0% |
| Trumbull, CT | 36,477 | 43 | 14.0% |
| Bedford Hills, NY | 2,892 | 43 | 14.0% |
| Norwalk, CT | 88,755 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| Newmarket, ON | 88,702 | n/a | |
| Nashua, NH | 89,052 | 37 | 26.0% |
| Conroe, TX | 88,369 | 52 | 4.0% |
| Chino, CA | 89,170 | 89 | 78.0% |
| Reading, PA | 88,333 | 42 | 16.0% |
| Norwalk, CT | 88,755 | 43 | 14.0% |
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