Boundary Layer Processes affecting pollutant transport and dispersion over a Complex-Terrain Coastal Region

Elevated pollutant layers are frequently observed over areas of complex terrain. These elevated plumes are a reservoir of high-concentration, aged pollutants that, when mixed down to the surface, can make significant contributions to surface concentration. The processes that produce the elevated layers are not yet clearly understood mainly due to lack of necessary observations. The Southern California Ozone Study (SCOS'97), sponsored by the California Air Resources Board and conducted in the Greater Los Angles Basin area in the summer and early fall of 1997, offers a rich data set that is unprecedented in spatial and temporal resolution for a coastal complex terrain area. In this research, we have assimilated data from 26 wind profiler/RASSes and 12 rawinsondes for the high ozone episode of 5-8 August during SCOS'97 into RAMS (the Regional Atmospheric Modeling System). From this, we were able to determine the evolving boundary layer structures and complex flow patterns that resulted from interactions between the large-scale winds, the local sea-breeze circulation, and the terrain-induced circulations. The meteorological simulations were then used to drive a Lagrangian particle dispersion model to identify the processes leading to the formation of elevated plumes and to assess the impact of the elevated plumes on surface concentrations.