| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 20°F | 39°F | 29°F | 3.5" |
| February | 21°F | 42°F | 31°F | 2.6" |
| March | 32°F | 55°F | 43°F | 4.0" |
| April | 42°F | 68°F | 55°F | 5.3" |
| May | 52°F | 76°F | 64°F | 4.8" |
| June | 62°F | 85°F | 73°F | 5.7" |
| July | 65°F | 87°F | 76°F | 4.9" |
| August | 65°F | 87°F | 75°F | 3.3" |
| September | 57°F | 81°F | 68°F | 3.4" |
| October | 45°F | 68°F | 56°F | 3.2" |
| November | 33°F | 55°F | 44°F | 3.3" |
| December | 25°F | 42°F | 33°F | 4.1" |
| Index | Monrovia | Indiana | National |
| Air quality index | 54 | 56 | 42 |
| Pollution index | 2,395,300 | 2,719,453 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 148 |
| Days with moderate air quality | 212 |
| Days w/ poor A.Q. for sensitive groups | 5 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.010% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Morgantown, IN | 1,352 | 42 | 16.0% |
| Painted Hills, IN | 525 | 42 | 16.0% |
| Paragon, IN | 467 | 42 | 16.0% |
| Martinsville, IN | 11,807 | 42 | 16.0% |
| Bethany, IN | 58 | 54 | 8.0% |
| Monrovia, IN | 1,383 | 54 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Highfill, AR | 1,383 | 44 | 12.0% |
| Harwich Center, MA | 1,383 | 36 | 28.0% |
| Bel Air CDP, MD | 1,383 | 46 | 8.0% |
| Coldstream, OH | 1,383 | 54 | 8.0% |
| Tiltonsville, OH | 1,383 | 39 | 22.0% |
| Monrovia, IN | 1,383 | 54 | 8.0% |
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