| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 31°F | 48°F | 38°F | 4.1" |
| February | 22°F | 45°F | 33°F | 3.8" |
| March | 31°F | 55°F | 41°F | 8.2" |
| April | 46°F | 69°F | 56°F | 11.0" |
| May | 56°F | 78°F | 66°F | 0.8" |
| June | 65°F | 83°F | 74°F | 12.8" |
| July | 68°F | 86°F | 76°F | 7.5" |
| August | 65°F | 85°F | 74°F | 5.1" |
| September | 61°F | 82°F | 70°F | 4.7" |
| October | 48°F | 71°F | 58°F | 13.4" |
| November | 38°F | 59°F | 46°F | 3.2" |
| December | 32°F | 50°F | 40°F | 7.1" |
| Index | Portsmouth | Ohio | National |
| Air quality index | 14 | 40 | 42 |
| Pollution index | 1,306,310 | 4,472,386 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 356 |
| Days with moderate air quality | 9 |
| Days w/ poor A.Q. for sensitive groups | 0 |
| Days with unhealthy air quality | 0 |
| Pollutant | Total |
| Arsenic | 0.010% |
| Benzene | 0.020% |
| Carbon Tetrachloride | 0.002% |
| Lead | 0.290% |
| Mercury | 0.120% |
| City | Population | Air Quality Index | National Avg. |
| Friendship, OH | 523 | 14 | 72.0% |
| McDermott, OH | 354 | 14 | 72.0% |
| New Boston, OH | 2,657 | 14 | 72.0% |
| Minford, OH | 378 | 14 | 72.0% |
| Worthington, KY | 1,639 | 14 | 72.0% |
| Portsmouth, OH | 20,094 | 14 | 72.0% |
| City | Population | Air Quality Index | National Avg. |
| Pittsburg, KS | 20,096 | 37 | 26.0% |
| East Northport, NY | 20,085 | 43 | 14.0% |
| Dixon, CA | 20,106 | 52 | 4.0% |
| La Cañada Flintridge, CA | 20,078 | 72 | 44.0% |
| Niagara-on-the-Lake, ON | 20,111 | n/a | |
| Portsmouth, OH | 20,094 | 14 | 72.0% |
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