| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 29°F | 44°F | 36°F | 4.8" |
| February | 29°F | 45°F | 36°F | 3.9" |
| March | 36°F | 54°F | 44°F | 5.5" |
| April | 47°F | 66°F | 55°F | 5.8" |
| May | 56°F | 73°F | 64°F | 6.3" |
| June | 67°F | 83°F | 74°F | 6.4" |
| July | 71°F | 86°F | 78°F | 6.7" |
| August | 70°F | 84°F | 77°F | 7.1" |
| September | 65°F | 80°F | 72°F | 5.9" |
| October | 53°F | 69°F | 61°F | 6.4" |
| November | 42°F | 58°F | 49°F | 5.2" |
| December | 33°F | 48°F | 40°F | 5.9" |
| Index | Arnold | Maryland | National |
| Air quality index | 46 | 43 | 42 |
| Pollution index | 3,494,010 | 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 | 0.010% |
| Benzene | 0.040% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.010% |
| Mercury | 0.001% |
| City | Population | Air Quality Index | National Avg. |
| Ferndale, MD | 17,732 | 46 | 8.0% |
| Linthicum, MD | 10,116 | 46 | 8.0% |
| Tolchester, MD | 435 | 46 | 8.0% |
| Chester, MD | 4,319 | 46 | 8.0% |
| Parole, MD | 17,505 | 46 | 8.0% |
| Arnold, MD | 24,334 | 46 | 8.0% |
| City | Population | Air Quality Index | National Avg. |
| Mequon, WI | 24,357 | 44 | 12.0% |
| Papillion, NE | 24,310 | 40 | 20.0% |
| Avon Lake, OH | 24,309 | 50 | = 100 |
| Palmetto Bay, FL | 24,308 | 41 | 18.0% |
| Wasaga Beach, ON | 24,372 | n/a | |
| Arnold, MD | 24,334 | 46 | 8.0% |
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