| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 45°F | 69°F | 56°F | 3.3" |
| February | 46°F | 70°F | 57°F | 2.5" |
| March | 49°F | 73°F | 60°F | 2.0" |
| April | 52°F | 75°F | 62°F | 0.6" |
| May | 56°F | 78°F | 65°F | 0.2" |
| June | 60°F | 83°F | 70°F | 0.0" |
| July | 65°F | 89°F | 75°F | 0.0" |
| August | 65°F | 90°F | 75°F | 0.0" |
| September | 63°F | 89°F | 74°F | 0.2" |
| October | 57°F | 82°F | 68°F | 0.5" |
| November | 50°F | 76°F | 62°F | 0.6" |
| December | 44°F | 68°F | 55°F | 2.1" |
| Index | Altadena | California | National |
| Air quality index | 72 | 55 | 42 |
| Pollution index | 139,490,000 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 66 |
| Days with moderate air quality | 208 |
| Days w/ poor A.Q. for sensitive groups | 62 |
| Days with unhealthy air quality | 28 |
| Pollutant | Total |
| Arsenic | 0.200% |
| Benzene | 0.950% |
| Carbon Tetrachloride | 0.080% |
| Lead | 1.320% |
| Mercury | 0.440% |
| City | Population | Air Quality Index | National Avg. |
| Commerce, CA | 12,738 | 72 | 44.0% |
| West Whittier-Los Nietos, CA | 26,121 | 72 | 44.0% |
| San Marino, CA | 13,020 | 72 | 44.0% |
| Duarte, CA | 21,399 | 72 | 44.0% |
| Mayflower Village, CA | 5,687 | 72 | 44.0% |
| Altadena, CA | 43,037 | 72 | 44.0% |
| City | Population | Air Quality Index | National Avg. |
| Freeport, NY | 42,993 | 51 | 2.0% |
| DeKalb, IL | 42,961 | 42 | 16.0% |
| Goose Creek, SC | 42,944 | 38 | 24.0% |
| Fond du Lac, WI | 42,944 | 36 | 28.0% |
| Winter Haven, FL | 42,933 | 36 | 28.0% |
| Altadena, CA | 43,037 | 72 | 44.0% |
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