| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 48°F | 70°F | 58°F | 3.5" |
| February | 50°F | 70°F | 59°F | 2.9" |
| March | 52°F | 72°F | 61°F | 1.5" |
| April | 55°F | 74°F | 63°F | 0.7" |
| May | 58°F | 75°F | 65°F | 0.5" |
| June | 61°F | 78°F | 68°F | 0.0" |
| July | 65°F | 83°F | 72°F | 0.0" |
| August | 65°F | 84°F | 73°F | 0.0" |
| September | 64°F | 85°F | 72°F | 0.3" |
| October | 60°F | 81°F | 69°F | 0.7" |
| November | 54°F | 75°F | 63°F | 0.8" |
| December | 48°F | 69°F | 57°F | 2.8" |
| Index | Monrovia | 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. |
| Industry, CA | 264 | 72 | 44.0% |
| South San Jose Hills, CA | 19,104 | 72 | 44.0% |
| West Covina, CA | 105,808 | 72 | 44.0% |
| La Crescenta-Montrose, CA | 20,171 | 72 | 44.0% |
| La Habra Heights, CA | 5,318 | 72 | 44.0% |
| Monrovia, CA | 37,636 | 72 | 44.0% |
| City | Population | Air Quality Index | National Avg. |
| Rock Island, IL | 37,651 | 46 | 8.0% |
| Carpentersville, IL | 37,618 | 55 | 10.0% |
| Menomonee Falls, WI | 37,611 | 44 | 12.0% |
| Clinton, MD | 37,765 | 47 | 6.0% |
| Egypt Lake-Leto, FL | 37,775 | 43 | 14.0% |
| Monrovia, CA | 37,636 | 72 | 44.0% |
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