| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 31°F | 48°F | 39°F | 7.2" |
| February | 25°F | 43°F | 34°F | 3.7" |
| March | 33°F | 54°F | 43°F | 7.2" |
| April | 42°F | 65°F | 53°F | 4.6" |
| May | 49°F | 73°F | 61°F | 7.3" |
| June | 63°F | 83°F | 72°F | 5.0" |
| July | 68°F | 87°F | 77°F | 8.6" |
| August | 68°F | 87°F | 77°F | 5.2" |
| September | 59°F | 84°F | 71°F | 1.4" |
| October | 53°F | 73°F | 62°F | 9.9" |
| November | 39°F | 61°F | 50°F | 4.3" |
| December | 30°F | 48°F | 39°F | 5.2" |
| Index | Bethel | Delaware | National |
| Air quality index | 36 | 41 | 42 |
| Pollution index | 7,219,540 | 7,274,307 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 303 |
| Days with moderate air quality | 61 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality |
| Pollutant | Total |
| Arsenic | 0.060% |
| Benzene | 0.070% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.030% |
| Mercury | 0.110% |
| City | Population | Air Quality Index | National Avg. |
| Bridgeville, DE | 3,508 | 36 | 28.0% |
| Delmar, MD | 3,321 | 36 | 28.0% |
| Eldorado, MD | 76 | 36 | 28.0% |
| Sharptown, MD | 687 | 36 | 28.0% |
| Quantico, MD | 199 | 36 | 28.0% |
| Bethel, DE | 404 | 36 | 28.0% |
| City | Population | Air Quality Index | National Avg. |
| Jenkinsburg, GA | 404 | 52 | 4.0% |
| Arrowsmith, IL | 404 | 44 | 12.0% |
| Walker, MO | 404 | 37 | 26.0% |
| Dumas, MS | 404 | 39 | 22.0% |
| Orleans, NE | 404 | 19 | 62.0% |
| Bethel, DE | 404 | 36 | 28.0% |
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