| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 25°F | 46°F | 34°F | 3.1" |
| February | 25°F | 47°F | 36°F | 2.7" |
| March | 33°F | 58°F | 45°F | 3.6" |
| April | 43°F | 70°F | 56°F | 3.8" |
| May | 52°F | 77°F | 65°F | 4.1" |
| June | 62°F | 86°F | 74°F | 4.7" |
| July | 67°F | 90°F | 78°F | 4.5" |
| August | 65°F | 88°F | 76°F | 4.7" |
| September | 58°F | 82°F | 70°F | 4.3" |
| October | 47°F | 70°F | 58°F | 5.7" |
| November | 36°F | 59°F | 47°F | 2.8" |
| December | 30°F | 50°F | 39°F | 4.3" |
| Index | Ellicott City | Maryland | National |
| Air quality index | 46 | 43 | 42 |
| Pollution index | 3,089,800 | 5,342,367 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 223 |
| Days with moderate air quality | 129 |
| Days w/ poor A.Q. for sensitive groups | 13 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.070% |
| Mercury | 0.010% |
| City | Population | Air Quality Index | National Avg. |
| Fort Meade, MD | 11,340 | 46 | 8.0% |
| Pasadena, MD | 29,432 | 46 | 8.0% |
| Elkridge, MD | 21,778 | 46 | 8.0% |
| Riviera Beach, MD | 12,780 | 46 | 8.0% |
| Carney, MD | 29,624 | 46 | 8.0% |
| Ellicott City, MD | 73,272 | 46 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Flagstaff, AZ | 73,319 | 45 | 10.0% |
| Apple Valley, CA | 73,339 | 89 | 78.0% |
| Schaumburg, IL | 73,392 | 55 | 10.0% |
| Bismarck, ND | 73,435 | 36 | 28.0% |
| St. Albert, AB | 73,103 | n/a | |
| Ellicott City, MD | 73,272 | 46 | 8.0% |
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