| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 44°F | 69°F | 56°F | 2.3" |
| February | 45°F | 70°F | 57°F | 2.0" |
| March | 48°F | 74°F | 60°F | 1.2" |
| April | 51°F | 77°F | 62°F | 0.7" |
| May | 55°F | 81°F | 66°F | 0.4" |
| June | 60°F | 88°F | 72°F | 0.0" |
| July | 65°F | 94°F | 77°F | 0.1" |
| August | 65°F | 95°F | 78°F | 0.0" |
| September | 64°F | 93°F | 76°F | 0.2" |
| October | 57°F | 84°F | 69°F | 0.4" |
| November | 49°F | 77°F | 62°F | 0.6" |
| December | 43°F | 68°F | 55°F | 2.6" |
| Index | Ontario | California | National |
| Air quality index | 89 | 55 | 42 |
| Pollution index | 22,790,900 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 42 |
| Days with moderate air quality | 178 |
| Days w/ poor A.Q. for sensitive groups | 79 |
| Days with unhealthy air quality | 58 |
| Pollutant | Total |
| Arsenic | 0.060% |
| Benzene | 0.190% |
| Carbon Tetrachloride | 0.010% |
| Lead | 0.220% |
| Mercury | 0.230% |
| City | Population | Air Quality Index | National Avg. |
| Azusa, CA | 49,584 | 72 | 44.0% |
| South San Jose Hills, CA | 19,104 | 72 | 44.0% |
| Citrus, CA | 10,105 | 72 | 44.0% |
| West Covina, CA | 105,808 | 72 | 44.0% |
| Rowland Heights, CA | 49,914 | 89 | 78.0% |
| Ontario, CA | 178,194 | 89 | 78.0% |
| City | Population | Air Quality Index | National Avg. |
| Rancho Cucamonga, CA | 178,060 | 89 | 78.0% |
| Santa Rosa, CA | 178,391 | 34 | 32.0% |
| Providence, RI | 179,472 | 44 | 12.0% |
| Newport News, VA | 179,582 | 40 | 20.0% |
| Oshawa, ON | 176,009 | n/a | |
| Ontario, CA | 178,194 | 89 | 78.0% |
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