| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 12°F | 26°F | 18°F | 0.5" |
| February | 13°F | 29°F | 20°F | 0.6" |
| March | 29°F | 44°F | 35°F | 1.4" |
| April | 40°F | 60°F | 48°F | 3.0" |
| May | 50°F | 71°F | 60°F | 3.0" |
| June | 60°F | 80°F | 69°F | 6.0" |
| July | 63°F | 82°F | 72°F | 4.7" |
| August | 61°F | 80°F | 70°F | 4.2" |
| September | 53°F | 75°F | 63°F | 5.0" |
| October | 42°F | 61°F | 50°F | 2.3" |
| November | 30°F | 46°F | 37°F | 1.1" |
| December | 16°F | 30°F | 23°F | 1.4" |
| Index | Ionia | Iowa | National |
| Air quality index | 39 | 39 | 42 |
| Pollution index | 530,484 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 363 |
| Days with good air quality | 286 |
| Days with moderate air quality | 77 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.000% |
| Benzene | 0.010% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.002% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Charles City, IA | 7,351 | 15 | 70.0% |
| Bassett, IA | 42 | 15 | 70.0% |
| Floyd, IA | 310 | 15 | 70.0% |
| Colwell, IA | 60 | 15 | 70.0% |
| Alta Vista, IA | 223 | 15 | 70.0% |
| Ionia, IA | 296 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| St. Joe, AR | 296 | 36 | 28.0% |
| Modale, IA | 296 | 40 | 20.0% |
| Alma, IL | 296 | 43 | 14.0% |
| Fillmore, IL | 296 | 40 | 20.0% |
| Belcher, LA | 296 | 39 | 22.0% |
| Ionia, IA | 296 | 39 | 22.0% |
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