| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 16°F | 34°F | 25°F | 2.3" |
| February | 18°F | 36°F | 27°F | 2.3" |
| March | 29°F | 49°F | 39°F | 2.8" |
| April | 38°F | 63°F | 50°F | 3.9" |
| May | 48°F | 73°F | 60°F | 5.4" |
| June | 59°F | 83°F | 71°F | 4.5" |
| July | 64°F | 86°F | 75°F | 5.2" |
| August | 63°F | 84°F | 74°F | 4.4" |
| September | 56°F | 78°F | 66°F | 3.6" |
| October | 44°F | 65°F | 54°F | 3.4" |
| November | 32°F | 52°F | 42°F | 2.3" |
| December | 21°F | 38°F | 29°F | 2.9" |
| Index | Harwood Heights | Illinois | National |
| Air quality index | 55 | 41 | 42 |
| Pollution index | 3,795,410 | 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 | 0.030% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.003% |
| Mercury | 0.310% |
| City | Population | Air Quality Index | National Avg. |
| Bellwood, IL | 18,799 | 55 | 10.0% |
| La Grange, IL | 15,555 | 55 | 10.0% |
| Melrose Park, IL | 25,404 | 55 | 10.0% |
| Lisle, IL | 23,363 | 55 | 10.0% |
| Justice, IL | 12,677 | 55 | 10.0% |
| Harwood Heights, IL | 8,393 | 55 | 10.0% |
| City | Population | Air Quality Index | National Avg. |
| Beaver Falls, PA | 8,393 | 6 | 88.0% |
| Kennedale, TX | 8,393 | 51 | 2.0% |
| Kalifornsky, AK | 8,395 | 31 | 38.0% |
| Warrenton, MO | 8,388 | 54 | 8.0% |
| Torbay, NL | 8,388 | n/a | |
| Harwood Heights, IL | 8,393 | 55 | 10.0% |
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