| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 3°F | 22°F | 12°F | 0.9" |
| February | 4°F | 25°F | 15°F | 1.0" |
| March | 17°F | 38°F | 28°F | 1.5" |
| April | 30°F | 52°F | 40°F | 2.5" |
| May | 40°F | 64°F | 51°F | 4.0" |
| June | 49°F | 74°F | 61°F | 4.7" |
| July | 56°F | 80°F | 68°F | 3.4" |
| August | 54°F | 77°F | 65°F | 4.5" |
| September | 47°F | 70°F | 58°F | 3.2" |
| October | 36°F | 55°F | 45°F | 3.2" |
| November | 23°F | 40°F | 31°F | 1.7" |
| December | 9°F | 25°F | 16°F | 1.7" |
| Index | Duluth | Minnesota | National |
| Air quality index | 35 | 35 | 42 |
| Pollution index | 1,760,360 | 1,854,519 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 326 |
| Days with moderate air quality | 38 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.030% |
| Lead | 0.010% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Hermantown, MN | 9,577 | 35 | 30.0% |
| Oliver, WI | 278 | 35 | 30.0% |
| Proctor, MN | 3,039 | 35 | 30.0% |
| Superior, WI | 26,260 | 35 | 30.0% |
| Carlton, MN | 1,006 | 35 | 30.0% |
| Duluth, MN | 85,852 | 35 | 30.0% |
| City | Population | Air Quality Index | National Avg. |
| Bryan, TX | 85,645 | 38 | 24.0% |
| Avondale, AZ | 86,091 | 74 | 48.0% |
| Hawthorne, CA | 85,410 | 72 | 44.0% |
| Hoover, AL | 85,386 | 53 | 6.0% |
| Bloomington, MN | 85,226 | 46 | 8.0% |
| Duluth, MN | 85,852 | 35 | 30.0% |
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