| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 34°F | 60°F | 46°F | 2.9" |
| February | 36°F | 63°F | 49°F | 3.7" |
| March | 43°F | 72°F | 57°F | 3.3" |
| April | 51°F | 80°F | 66°F | 3.1" |
| May | 59°F | 86°F | 72°F | 3.2" |
| June | 69°F | 92°F | 80°F | 5.2" |
| July | 72°F | 94°F | 82°F | 5.4" |
| August | 72°F | 93°F | 81°F | 6.1" |
| September | 65°F | 88°F | 76°F | 3.5" |
| October | 52°F | 79°F | 65°F | 4.0" |
| November | 40°F | 69°F | 54°F | 3.2" |
| December | 38°F | 63°F | 50°F | 4.6" |
| Index | Irmo | South Carolina | National |
| Air quality index | 43 | 37 | 42 |
| Pollution index | 13,023,700 | 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 | 2.600% |
| Benzene | 0.080% |
| Carbon Tetrachloride | 0.060% |
| Lead | 0.120% |
| Mercury | 0.110% |
| City | Population | Air Quality Index | National Avg. |
| Dentsville, SC | 15,537 | 43 | 14.0% |
| Columbia, SC | 134,057 | 43 | 14.0% |
| St. Andrews, SC | 21,355 | 43 | 14.0% |
| Springdale, SC | 2,878 | 43 | 14.0% |
| Jenkinsville, SC | 36 | 43 | 14.0% |
| Irmo, SC | 12,397 | 43 | 14.0% |
| City | Population | Air Quality Index | National Avg. |
| Summerland, BC | 12,400 | n/a | |
| Markham, IL | 12,401 | 55 | 10.0% |
| Patchogue, NY | 12,389 | 43 | 14.0% |
| Brock, ON | 12,406 | n/a | |
| Sidney, BC | 12,386 | n/a | |
| Irmo, SC | 12,397 | 43 | 14.0% |
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