| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 36°F | 57°F | 45°F | 4.9" |
| February | 35°F | 58°F | 46°F | 8.7" |
| March | 43°F | 68°F | 55°F | 9.3" |
| April | 47°F | 72°F | 59°F | 8.7" |
| May | 56°F | 81°F | 68°F | 6.6" |
| June | 66°F | 88°F | 76°F | 6.3" |
| July | 69°F | 88°F | 77°F | 12.9" |
| August | 71°F | 93°F | 80°F | 9.3" |
| September | 65°F | 87°F | 75°F | 4.1" |
| October | 54°F | 76°F | 64°F | 6.4" |
| November | 41°F | 66°F | 52°F | 4.0" |
| December | 36°F | 56°F | 45°F | 8.1" |
| Index | Decatur | Georgia | National |
| Air quality index | 52 | 41 | 42 |
| Pollution index | 19,982,200 | 1,874,972 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 162 |
| Days with moderate air quality | 184 |
| Days w/ poor A.Q. for sensitive groups | 18 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.210% |
| Benzene | 0.260% |
| Carbon Tetrachloride | 0.050% |
| Lead | 0.100% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Hapeville, GA | 6,576 | 52 | 4.0% |
| Avondale Estates, GA | 3,142 | 52 | 4.0% |
| Doraville, GA | 10,244 | 52 | 4.0% |
| Forest Park, GA | 19,884 | 52 | 4.0% |
| North Decatur, GA | 15,833 | 52 | 4.0% |
| Decatur, GA | 24,814 | 52 | 4.0% |
| City | Population | Air Quality Index | National Avg. |
| Paris, TX | 24,814 | 325 | 550.0% |
| Hazleton, PA | 24,804 | 38 | 24.0% |
| Clinton, MS | 24,797 | 44 | 12.0% |
| Ardmore, OK | 24,834 | 43 | 14.0% |
| Rosemount, MN | 24,792 | 46 | 8.0% |
| Decatur, GA | 24,814 | 52 | 4.0% |
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