Use of atmospheric dispersion models to assess pollutant impacts in complex terrain is increasing. However, the temporally and spatially varying wind and turbulence fields in mountainous areas often invalidate the assumptions of straight-line flow and horizontal homogeneity inherent in standard plume models. A dispersion model was recently developed at the Rocky Flats Plant to realistically simulate dispersion processes in complex terrain. The new model treats pollutant releases as a series of overlapping ellipsoidal puffs. The ends of each puff axis are defined by ''tracer'' particles, which are independently advected through the modeled windfield. The puff axes are not, in general, orthogonal. Thus, a puff can develop an arbitrary shape in response to differential diffusion rates, horizontal convergence and divergence, vertical shear, surface reflection, and gravitational settling. The model includes modules for puff transport, diffusion, wet and dry deposition, resuspension, surface roughness effects, ingrowth, decay, and external and internal dosimetry. This report focuses on the simulation of puff growth and shape.
