| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 26°F | 42°F | 34°F | 6.3" |
| February | 24°F | 42°F | 32°F | 4.9" |
| March | 31°F | 50°F | 40°F | 7.3" |
| April | 46°F | 67°F | 55°F | 5.0" |
| May | 56°F | 76°F | 65°F | 9.9" |
| June | 64°F | 83°F | 73°F | 8.3" |
| July | 71°F | 87°F | 78°F | 8.3" |
| August | 67°F | 84°F | 75°F | 7.8" |
| September | 61°F | 80°F | 70°F | 4.9" |
| October | 54°F | 72°F | 62°F | 6.3" |
| November | 38°F | 56°F | 46°F | 5.9" |
| December | 33°F | 46°F | 39°F | 5.8" |
| Index | Iselin | New Jersey | National |
| Air quality index | 51 | 45 | 42 |
| Pollution index | 12,837,200 | 7,246,891 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 169 |
| Days with moderate air quality | 180 |
| Days w/ poor A.Q. for sensitive groups | 16 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.110% |
| Carbon Tetrachloride | 0.050% |
| Lead | 0.020% |
| Mercury | 0.230% |
| City | Population | Air Quality Index | National Avg. |
| Mendham, NJ | 4,880 | 34 | 32.0% |
| Griggstown, NJ | 858 | 41 | 18.0% |
| Pleasant Plains, NJ | 627 | 41 | 18.0% |
| Finderne, NJ | 5,775 | 41 | 18.0% |
| Somerville, NJ | 12,139 | 41 | 18.0% |
| Iselin, NJ | 17,356 | 51 | 2.0% |
| City | Population | Air Quality Index | National Avg. |
| Hinsdale, IL | 17,366 | 55 | 10.0% |
| Oswego, NY | 17,371 | 37 | 26.0% |
| L'Ancienne-Lorette, QC | 17,373 | n/a | |
| Nederland, TX | 17,334 | 45 | 10.0% |
| Estelle, LA | 17,330 | 45 | 10.0% |
| Iselin, NJ | 17,356 | 51 | 2.0% |
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