| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 35°F | 58°F | 45°F | 5.9" |
| February | 37°F | 63°F | 49°F | 6.6" |
| March | 44°F | 70°F | 56°F | 7.3" |
| April | 53°F | 78°F | 65°F | 6.5" |
| May | 61°F | 84°F | 72°F | 6.9" |
| June | 69°F | 91°F | 79°F | 6.7" |
| July | 72°F | 92°F | 81°F | 9.1" |
| August | 70°F | 91°F | 79°F | 8.3" |
| September | 65°F | 87°F | 74°F | 11.1" |
| October | 53°F | 78°F | 64°F | 7.9" |
| November | 41°F | 68°F | 53°F | 7.0" |
| December | 40°F | 63°F | 50°F | 8.0" |
| Index | Barnwell | South Carolina | National |
| Air quality index | 47 | 37 | 42 |
| Pollution index | 6,343,880 | 3,620,438 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 219 |
| Days with moderate air quality | 144 |
| Days w/ poor A.Q. for sensitive groups | 2 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.050% |
| Benzene | 0.050% |
| Carbon Tetrachloride | 0.090% |
| Lead | 0.010% |
| Mercury | 0.100% |
| City | Population | Air Quality Index | National Avg. |
| Govan, SC | 60 | 29 | 42.0% |
| Hilda, SC | 461 | 29 | 42.0% |
| Ulmer, SC | 85 | 29 | 42.0% |
| Kline, SC | 150 | 29 | 42.0% |
| Denmark, SC | 3,231 | 29 | 42.0% |
| Barnwell, SC | 4,373 | 47 | 6.0% |
| City | Population | Air Quality Index | National Avg. |
| Hampden, ME | 4,373 | 31 | 38.0% |
| Okauchee Lake, WI | 4,373 | 37 | 26.0% |
| La Joya, TX | 4,374 | 42 | 16.0% |
| North Terre Haute, IN | 4,371 | 45 | 10.0% |
| Isle of Palms, SC | 4,371 | 38 | 24.0% |
| Barnwell, SC | 4,373 | 47 | 6.0% |
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