Adaptation of the QUIC-PLUME model for heavy gas dispersion around buildings

A fast running, urban atmospheric plume transport and dispersion model is needed for many aspects of preparation, training, assessment, and response in case of intentional or accidental releases of toxic agents in a city. We are developing the QUIC (Quick Urban & Industrial Complex) dispersion modeling system to meet these needs. The QUIC-URB wind model computes 3D wind fields around buildings, while the QUIC-PLUME dispersion model computes airborne concentrations and deposition on building and street surfaces. The dispersion model, QUIC-PLUME, is based on a non-standard version of the Lagrangian random-walk equations that allows it to account for horizontally-inhomogeneous turbulence found in built-up areas. QUIC-PLUME includes a treatment of non-local mixing and the turbulence induced by non-zero vertical winds or wind speed gradients in the horizontal plane. We have recently revised the model to treat dispersion of dense gases and tested the model against field data. Heavy gas dispersion poses a challenge for random-walk dispersion models because the transport of individual pollutant parcels is inextricably linked to the collective behavior of all parcels. We describe the methods for meeting this challenge and compare model results to measurements.