| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 38°F | 28°F | 3.4" |
| February | 20°F | 40°F | 30°F | 2.3" |
| March | 31°F | 53°F | 41°F | 4.0" |
| April | 41°F | 67°F | 53°F | 4.5" |
| May | 51°F | 75°F | 63°F | 4.1" |
| June | 61°F | 84°F | 72°F | 4.5" |
| July | 63°F | 85°F | 74°F | 4.3" |
| August | 62°F | 85°F | 73°F | 2.9" |
| September | 55°F | 79°F | 67°F | 4.3" |
| October | 44°F | 67°F | 55°F | 3.5" |
| November | 33°F | 55°F | 43°F | 3.1" |
| December | 25°F | 42°F | 33°F | 3.9" |
| Index | Vandalia | Ohio | National |
| Air quality index | 47 | 40 | 42 |
| Pollution index | 11,539,300 | 4,472,386 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 213 |
| Days with moderate air quality | 152 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.210% |
| Benzene | 0.110% |
| Carbon Tetrachloride | 0.060% |
| Lead | 0.110% |
| Mercury | 0.050% |
| City | Population | Air Quality Index | National Avg. |
| Donnelsville, OH | 329 | 45 | 10.0% |
| New Carlisle, OH | 5,577 | 45 | 10.0% |
| Holiday Valley, OH | 1,573 | 45 | 10.0% |
| Christiansburg, OH | 481 | 45 | 10.0% |
| Enon, OH | 2,517 | 45 | 10.0% |
| Vandalia, OH | 15,021 | 47 | 6.0% |
| City | Population | Air Quality Index | National Avg. |
| Belvedere Park, GA | 15,028 | 52 | 4.0% |
| Hugo, MN | 15,008 | 46 | 8.0% |
| Stone Ridge, VA | 15,034 | 47 | 6.0% |
| Williamsburg, VA | 15,034 | 44 | 12.0% |
| West Haven, UT | 15,003 | 45 | 10.0% |
| Vandalia, OH | 15,021 | 47 | 6.0% |
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