| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 36°F | 58°F | 46°F | 5.2" |
| February | 37°F | 61°F | 48°F | 6.7" |
| March | 44°F | 70°F | 56°F | 5.9" |
| April | 53°F | 78°F | 65°F | 7.0" |
| May | 60°F | 84°F | 72°F | 6.7" |
| June | 69°F | 91°F | 79°F | 9.9" |
| July | 72°F | 93°F | 81°F | 10.2" |
| August | 71°F | 91°F | 80°F | 7.7" |
| September | 65°F | 86°F | 75°F | 9.1" |
| October | 54°F | 77°F | 64°F | 12.0" |
| November | 43°F | 67°F | 54°F | 6.9" |
| December | 39°F | 62°F | 50°F | 7.2" |
| Index | Sumter | South Carolina | National |
| Air quality index | 43 | 37 | 42 |
| Pollution index | 4,798,360 | 3,620,438 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 264 |
| Days with moderate air quality | 99 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.002% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.001% |
| Mercury | 0.002% |
| City | Population | Air Quality Index | National Avg. |
| Mayesville, SC | 674 | 40 | 20.0% |
| Alcolu, SC | 413 | 40 | 20.0% |
| Oswego, SC | 197 | 40 | 20.0% |
| East Sumter, SC | 1,208 | 40 | 20.0% |
| Oakland, SC | 1,265 | 43 | 14.0% |
| Sumter, SC | 39,758 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| La Puente, CA | 39,780 | 72 | 44.0% |
| Hallandale Beach, FL | 39,782 | 41 | 18.0% |
| New Berlin, WI | 39,794 | 44 | 12.0% |
| Vineyard, CA | 39,800 | 52 | 4.0% |
| Crystal Lake, IL | 39,685 | 42 | 16.0% |
| Sumter, SC | 39,758 | 43 | 14.0% |
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