Abstract
Abstract : The objective of this study was to improve scientists' understanding of dispersion in the planetary boundary layer, particularly the convective boundary layer (CBL), using Lagrangian particle models coupled with large-eddy simulation (LES) fields. A one-particle model for the mean concentration field was enhanced by a theoretically improved treatment of the LES subgrid-scale (SGS) velocities. The new model agreed with laboratory and field data and surface layer similarity theory. Investigations of stability effects on CBL dispersion showed that the dispersion rate decreased with a decreasing stability index -z(i)/L, which was attributed to the greater wind shear and the smaller turbulence scales in the surface layer. Using a two-particle model, the authors investigated relative dispersion in the CBL and found that it behaved in a quasi-homogeneous manner for all source heights except those near the surface; the latter was due to the vertical inhomogeneity in the dissipation rate. A study of concentration fluctuations revealed the large (factor of ^ 10) variability caused by velocity field fluctuations; the predicted concentration variability matched the trends in field observations from CBL sources. (11 figures, 36 refs.)
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