| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 34°F | 26°F | 1.9" |
| February | 21°F | 36°F | 28°F | 1.6" |
| March | 33°F | 49°F | 40°F | 2.4" |
| April | 42°F | 62°F | 51°F | 3.6" |
| May | 52°F | 73°F | 61°F | 4.3" |
| June | 63°F | 82°F | 72°F | 4.6" |
| July | 68°F | 86°F | 76°F | 3.5" |
| August | 67°F | 83°F | 75°F | 5.1" |
| September | 60°F | 77°F | 68°F | 2.8" |
| October | 48°F | 65°F | 55°F | 3.9" |
| November | 36°F | 51°F | 43°F | 2.2" |
| December | 25°F | 37°F | 31°F | 2.2" |
| Index | Berwyn | Illinois | National |
| Air quality index | 55 | 41 | 42 |
| Pollution index | 4,766,000 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 121 |
| Days with moderate air quality | 227 |
| Days w/ poor A.Q. for sensitive groups | 16 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.060% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.020% |
| Mercury | 0.090% |
| City | Population | Air Quality Index | National Avg. |
| Brookfield, IL | 18,520 | 55 | 10.0% |
| Forest Park, IL | 13,808 | 55 | 10.0% |
| Blue Island, IL | 23,160 | 55 | 10.0% |
| Dixmoor, IL | 3,570 | 55 | 10.0% |
| Posen, IL | 5,772 | 55 | 10.0% |
| Berwyn, IL | 54,850 | 55 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Cathedral City, CA | 54,812 | 89 | 78.0% |
| Lenexa, KS | 54,804 | 47 | 6.0% |
| Brookhaven, GA | 54,727 | 52 | 4.0% |
| Port Arthur, TX | 54,705 | 45 | 10.0% |
| Normal, IL | 54,699 | 44 | 12.0% |
| Berwyn, IL | 54,850 | 55 | 10.0% |
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