| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 23°F | 42°F | 32°F | 5.6" |
| February | 25°F | 45°F | 34°F | 3.8" |
| March | 37°F | 59°F | 47°F | 7.1" |
| April | 47°F | 70°F | 57°F | 10.2" |
| May | 56°F | 77°F | 66°F | 8.9" |
| June | 65°F | 87°F | 76°F | 9.2" |
| July | 68°F | 89°F | 78°F | 8.0" |
| August | 66°F | 88°F | 76°F | 7.8" |
| September | 58°F | 82°F | 69°F | 8.4" |
| October | 47°F | 70°F | 57°F | 8.6" |
| November | 36°F | 57°F | 46°F | 6.9" |
| December | 28°F | 45°F | 36°F | 8.2" |
| Index | Troy | Illinois | National |
| Air quality index | 54 | 41 | 42 |
| Pollution index | 6,055,640 | 3,148,694 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 134 |
| Days with moderate air quality | 221 |
| Days w/ poor A.Q. for sensitive groups | 8 |
| Days with unhealthy air quality | 2 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.040% |
| Lead | 0.100% |
| Mercury | 0.230% |
| City | Population | Air Quality Index | National Avg. |
| Mascoutah, IL | 8,454 | 54 | 8.0% |
| Centreville, IL | 4,946 | 54 | 8.0% |
| Collinsville, IL | 24,489 | 54 | 8.0% |
| East St. Louis, IL | 26,359 | 54 | 8.0% |
| Sauget, IL | 233 | 54 | 8.0% |
| Troy, IL | 10,278 | 54 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Pella, IA | 10,279 | 39 | 22.0% |
| Arden Hills, MN | 10,276 | 46 | 8.0% |
| Gig Harbor, WA | 10,280 | 18 | 64.0% |
| Bee Ridge, FL | 10,283 | 38 | 24.0% |
| Mapleton, UT | 10,270 | 46 | 8.0% |
| Troy, IL | 10,278 | 54 | 8.0% |
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