| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 40°F | 32°F | 2.6" |
| February | 23°F | 41°F | 32°F | 2.8" |
| March | 30°F | 48°F | 39°F | 3.4" |
| April | 40°F | 60°F | 50°F | 4.5" |
| May | 50°F | 69°F | 59°F | 3.8" |
| June | 60°F | 78°F | 68°F | 4.7" |
| July | 66°F | 84°F | 75°F | 3.1" |
| August | 64°F | 82°F | 74°F | 3.7" |
| September | 58°F | 77°F | 67°F | 3.2" |
| October | 47°F | 66°F | 57°F | 4.5" |
| November | 37°F | 55°F | 46°F | 2.9" |
| December | 30°F | 45°F | 37°F | 4.2" |
| Index | New Haven | Connecticut | National |
| Air quality index | 41 | 43 | 42 |
| Pollution index | 14,500,300 | 8,629,883 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 280 |
| Days with moderate air quality | 71 |
| Days w/ poor A.Q. for sensitive groups | 12 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.030% |
| Benzene | 0.140% |
| Carbon Tetrachloride | 0.050% |
| Lead | 0.080% |
| Mercury | 0.060% |
| City | Population | Air Quality Index | National Avg. |
| Durham, CT | 3,542 | 41 | 18.0% |
| Derby, CT | 12,420 | 41 | 18.0% |
| East Haven, CT | 28,645 | 41 | 18.0% |
| Naugatuck, CT | 31,201 | 41 | 18.0% |
| Shelton, CT | 41,162 | 41 | 18.0% |
| New Haven, CT | 130,381 | 41 | 18.0% |
| City | Population | Air Quality Index | National Avg. |
| Stamford, CT | 130,057 | 43 | 14.0% |
| Kent, WA | 130,038 | 45 | 10.0% |
| Concord, CA | 129,227 | 40 | 20.0% |
| Round Rock, TX | 128,812 | 44 | 12.0% |
| Langley, BC | 132,088 | n/a | |
| New Haven, CT | 130,381 | 41 | 18.0% |
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