| 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 | 39 | 39 | 42 |
| Pollution index | 5,075,380 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 287 |
| Days with moderate air quality | 78 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.070% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 2.000% |
| Lead | 0.040% |
| Mercury | 0.100% |
| City | Population | Air Quality Index | National Avg. |
| Central City, IA | 1,207 | 39 | 22.0% |
| Shueyville, IA | 795 | 39 | 22.0% |
| Mount Vernon, IA | 4,487 | 39 | 22.0% |
| Alburnett, IA | 812 | 39 | 22.0% |
| Ely, IA | 2,224 | 39 | 22.0% |
| Marion, IA | 39,910 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Streamwood, IL | 39,917 | 55 | 10.0% |
| Friendswood, TX | 39,893 | 52 | 4.0% |
| Chelsea, MA | 39,878 | 43 | 14.0% |
| The Acreage, FL | 39,863 | 36 | 28.0% |
| Calexico, CA | 39,841 | 58 | 16.0% |
| Marion, IA | 39,910 | 39 | 22.0% |
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