| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 10°F | 33°F | 21°F | 0.7" |
| February | 13°F | 38°F | 24°F | 0.8" |
| March | 26°F | 53°F | 38°F | 1.5" |
| April | 37°F | 66°F | 51°F | 3.5" |
| May | 48°F | 77°F | 62°F | 4.2" |
| June | 59°F | 86°F | 72°F | 4.9" |
| July | 63°F | 89°F | 76°F | 3.5" |
| August | 60°F | 86°F | 73°F | 5.6" |
| September | 51°F | 81°F | 65°F | 3.1" |
| October | 38°F | 68°F | 52°F | 3.0" |
| November | 25°F | 53°F | 38°F | 1.1" |
| December | 13°F | 36°F | 24°F | 1.7" |
| Index | Merrill | Iowa | National |
| Air quality index | 35 | 39 | 42 |
| Pollution index | 731,145 | 1,154,535 | 2,726,193 |
| Measurement | Total |
| Days measured | 364 |
| Days with good air quality | 322 |
| Days with moderate air quality | 42 |
| 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 | 0.002% |
| Lead | 0.002% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Oyens, IA | 100 | 35 | 30.0% |
| Le Mars, IA | 10,012 | 35 | 30.0% |
| Remsen, IA | 1,802 | 35 | 30.0% |
| Hinton, IA | 805 | 35 | 30.0% |
| Chatsworth, IA | 56 | 35 | 30.0% |
| Merrill, IA | 1,016 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| Burrton, KS | 1,016 | 40 | 20.0% |
| Mount Vernon, MD | 1,016 | 41 | 18.0% |
| New Franklin, MO | 1,016 | 38 | 24.0% |
| Greene, RI | 1,016 | 44 | 12.0% |
| Hewitt, WI | 1,016 | 34 | 32.0% |
| Merrill, IA | 1,016 | 35 | 30.0% |
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