Tracking the Sacramento Pollutant Plume over the Western Sierra Nevada

摘要

The pollution plume from Sacramento is often directed over the Sierra Nevada211u001efoothills east-northeast of the city where the highest local concentrations of 211u001eozone are typically experienced. This study used an aircraft instrumented to 211u001emeasure meteorological conditions, ozone and other pollutants to examine the 3-211u001edimensional nature of this plume. The aircraft was flown along three vertical 211u001eplanes oriented perpendicular to the upslope flow at 40, 80, and 120 km downwind 211u001eof the city, three times each day. A fourth flight measured the same information 211u001eat 40 and 80 km downwind. These measurements, as well as those documenting the 211u001emeteorological setting and evolution of surface conditions, are presented. High 211u001eresidual ozone above the surface layer in the early morning hours appears to be 211u001enecessary to produce afternoon concentrations in excess of 125 ppbv. The 211u001emoderately polluted days were characterized by low residual pollutant 211u001econcentrations aloft in the early morning and moderate to weak vertical 211u001estratification during the day. The cleaner days had good ventilation with deep 211u001elayers of near stratification and moderate to strong winds. The maximum ozone 211u001econcentrations were frequently observed in the afternoon, 40 to 80 km downwind of 211u001ethe city.