Research Projects

Project at a Glance

Project Status: complete

Report Published March 1998:

Title: Tracking the Sacramento pollutant plume over the western Sierra Nevada.

Principal Investigator / Author(s): Carroll, John J

Contractor: University of California, Davis

Contract Number: 94-334


Research Program Area: Atmospheric Processes

Topic Areas: Monitoring, Transport


Abstract:

The Sacramento area has an ozone air quality problem, exceeding the federal ambient air quality standard about a dozen days per year. Model simulation of events exceeding the standard has been less than desirable, in part due to the lack of knowledge of the three-dimensional distribution of meteorological and air quality variables. Given the city's location and climatic characteristics, the pollution plume from Sacramento is often directed over the Sierra Foothills east-northeast of the city, with this area typically experiencing the highest local concentrations of ozone and other secondary pollutants. This study used an aircraft instrumented to measure meteorological conditions, ozone and other pollutants to examine this plume. The aircraft was flown along three vertical planes oriented perpendicular to the upslope flow at 40, 80 and 120 km downwind of the city, three times each day. A fourth flight measured the same information at 40 and 80 km downwind. These flights were conducted on seven days in the summers of 1995 and 1996. These measurements, as well as those documenting the meteorological setting and evolution of surface conditions, are presented. High residual ozone above the surface layer in the early morning hours appears to be necessary to produce afternoon concentrations in excess of 125 ppbv. The moderately polluted days were characterized by low residual pollutant concentrations aloft in the early morning and moderate to weak vertical stratification during the day. The cleaner days had good ventilation with deep layers of near neutral stratification and moderate to strong winds. The maximum ozone concentrations were frequently observed in the afternoon, 40 to 80 km downwind of the city.


 

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