| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 12°F | 29°F | 20°F | 0.8" |
| February | 14°F | 32°F | 23°F | 1.0" |
| March | 28°F | 48°F | 37°F | 2.1" |
| April | 39°F | 63°F | 50°F | 4.6" |
| May | 50°F | 73°F | 61°F | 3.9" |
| June | 60°F | 81°F | 70°F | 7.0" |
| July | 63°F | 84°F | 73°F | 4.8" |
| August | 61°F | 82°F | 71°F | 4.7" |
| September | 53°F | 76°F | 64°F | 4.0" |
| October | 42°F | 63°F | 52°F | 3.1" |
| November | 29°F | 49°F | 38°F | 2.1" |
| December | 17°F | 33°F | 25°F | 1.9" |
| Index | Marion | Iowa | National |
| Air quality index | 42 | 39 | 50 |
| Pollution index | 5,075,380 | 1,643,836 | 5,066,862 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 256 |
| Days with moderate air quality | 108 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality |
| Pollutant | Total |
| Arsenic | 0.070% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 2.000% |
| Lead | 0.040% |
| Mercury | 0.100% |
| City, State | Population | Air Quality Index | National Avg. |
| Bertram, IA | 341 | 42 | 16% |
| Ely, IA | 2,133 | 42 | 16% |
| Martelle, IA | 266 | 42 | 16% |
| Robins, IA | 3,434 | 42 | 16% |
| Stone City, IA | 288 | 42 | 16% |
| Marion, IA | 37,198 | 42 | 16% |
| City, State | Population | Air Quality Index | National Avg. |
| Mechanicsville, VA | 37,201 | 39 | 22% |
| Addison, IL | 37,192 | 60 | 20% |
| East Meadow, NY | 37,228 | 53 | 6% |
| Lincoln Park, MI | 37,155 | 52 | 4% |
| Calumet City, IL | 37,112 | 60 | 20% |
| Marion, IA | 37,198 | 42 | 16% |