Lagrangian dispersion model for nonneutrally buoyant plumes

A capability to address positive and negative buoyancy was added to the Higher-Order Turbulence Model for Atmospheric Circulation-Random Puff Transport and Diffusion (HOTMAC-RAPTAD) modeling system. The modeling system was applied to simulate dense gas plumes, and the modeled concentrations were compared with observations reported in the Modelers' Data Archives (MDA). Sampling sites reported in MDA were located mostly 50-800 m from the source over flat terrain. To detect a peak concentration. RAPTAD sampling sites were placed on the arcs whose radii correspond to the sampling distance repot ted in MDA. Concentration averaging time for a peak concentration was varied from 1 to 600 s. RAPTAD simulation time varied from 4 to 30 min. The overall performance of the current model in terms of geometric mean biases, geometric variances, and residual plots was found to be at least as good as those of the better models examined previously with the same dataset.