| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 34°F | 57°F | 44°F | 4.7" |
| February | 32°F | 56°F | 43°F | 4.9" |
| March | 40°F | 67°F | 53°F | 9.2" |
| April | 46°F | 73°F | 59°F | 5.1" |
| May | 54°F | 80°F | 67°F | 3.1" |
| June | 65°F | 87°F | 75°F | 7.7" |
| July | 69°F | 90°F | 78°F | 6.0" |
| August | 71°F | 93°F | 81°F | 3.6" |
| September | 63°F | 88°F | 75°F | 1.5" |
| October | 54°F | 77°F | 64°F | 3.9" |
| November | 39°F | 66°F | 52°F | 4.6" |
| December | 34°F | 58°F | 44°F | 7.2" |
| Index | Irwin | South Carolina | National |
| Air quality index | 49 | 37 | 42 |
| Pollution index | 2,035,010 | 3,620,438 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 200 |
| Days with moderate air quality | 147 |
| Days w/ poor A.Q. for sensitive groups | 18 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.020% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.010% |
| Mercury | 0.004% |
| City | Population | Air Quality Index | National Avg. |
| Great Falls, SC | 1,806 | 43 | 14.0% |
| Heath Springs, SC | 639 | 43 | 14.0% |
| Kershaw, SC | 1,765 | 43 | 14.0% |
| Lesslie, SC | 3,185 | 49 | 2.0% |
| Fort Lawn, SC | 974 | 49 | 2.0% |
| Irwin, SC | 1,308 | 49 | 2.0% |
| City | Population | Air Quality Index | National Avg. |
| Bagley, MN | 1,308 | 33 | 34.0% |
| Mogul, NV | 1,308 | 46 | 8.0% |
| Miltonvale Park, PE | 1,308 | n/a | |
| Saint-Mathieu-du-Parc, QC | 1,308 | n/a | |
| Sifton, MB | 1,308 | n/a | |
| Irwin, SC | 1,308 | 49 | 2.0% |
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