| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 26°F | 45°F | 35°F | 4.6" |
| February | 27°F | 48°F | 37°F | 4.1" |
| March | 36°F | 59°F | 47°F | 5.4" |
| April | 45°F | 70°F | 57°F | 6.6" |
| May | 54°F | 77°F | 66°F | 7.2" |
| June | 63°F | 86°F | 74°F | 10.2" |
| July | 67°F | 89°F | 78°F | 8.7" |
| August | 66°F | 87°F | 76°F | 7.4" |
| September | 59°F | 81°F | 69°F | 11.4" |
| October | 48°F | 70°F | 58°F | 8.8" |
| November | 37°F | 59°F | 47°F | 5.7" |
| December | 31°F | 50°F | 40°F | 5.9" |
| Index | Merrifield | Virginia | National |
| Air quality index | 47 | 58 | 42 |
| Pollution index | 208,434 | 1,561,881 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 209 |
| Days with moderate air quality | 145 |
| Days w/ poor A.Q. for sensitive groups | 10 |
| Days with unhealthy air quality | 1 |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.002% |
| Carbon Tetrachloride | 0.001% |
| Lead | 0.001% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Glenmont, MD | 15,111 | 47 | 6.0% |
| Rockville, MD | 68,155 | 47 | 6.0% |
| Accokeek, MD | 11,590 | 47 | 6.0% |
| Mason Neck, VA | 1,938 | 47 | 6.0% |
| Dunn Loring, VA | 9,217 | 47 | 6.0% |
| Merrifield, VA | 18,523 | 47 | 6.0% |
| City | Population | Air Quality Index | National Avg. |
| Lake Shore, MD | 18,523 | 46 | 8.0% |
| Concord, MO | 18,521 | 54 | 8.0% |
| Brookfield, IL | 18,520 | 55 | 10.0% |
| Winchester, KY | 18,520 | 42 | 16.0% |
| Milledgeville, GA | 18,526 | 38 | 24.0% |
| Merrifield, VA | 18,523 | 47 | 6.0% |
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