| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 46°F | 70°F | 57°F | 2.6" |
| February | 48°F | 70°F | 58°F | 2.5" |
| March | 51°F | 72°F | 60°F | 1.0" |
| April | 53°F | 74°F | 62°F | 0.6" |
| May | 57°F | 75°F | 65°F | 0.3" |
| June | 61°F | 78°F | 67°F | 0.0" |
| July | 65°F | 83°F | 71°F | 0.2" |
| August | 65°F | 85°F | 72°F | 0.0" |
| September | 63°F | 85°F | 72°F | 0.3" |
| October | 59°F | 81°F | 68°F | 0.5" |
| November | 52°F | 76°F | 62°F | 0.7" |
| December | 46°F | 69°F | 56°F | 2.7" |
| Index | Downey | 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. |
| Azusa, CA | 49,584 | 72 | 44.0% |
| La Puente, CA | 39,780 | 72 | 44.0% |
| Vincent, CA | 16,405 | 72 | 44.0% |
| Gardena, CA | 59,401 | 72 | 44.0% |
| Westmont, CA | 35,188 | 72 | 44.0% |
| Downey, CA | 111,263 | 72 | 44.0% |
| City | Population | Air Quality Index | National Avg. |
| Lowell, MA | 111,311 | 37 | 26.0% |
| Pompano Beach, FL | 111,202 | 41 | 18.0% |
| Centennial, CO | 111,331 | 58 | 16.0% |
| Antioch, CA | 111,468 | 45 | 10.0% |
| Thunder Bay, ON | 111,499 | n/a | |
| Downey, CA | 111,263 | 72 | 44.0% |
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