Simulation of transport and dispersion of pollutants from elevated point sources in Mississippi Gulf coast using a Mesoscale atmospheric dispersion modeling system

A mesoscale atmospheric dispersion modeling system consisting of Weather Research and Forecast Model (WRF) and a 3-dimensional Lagrangian particle Dispersion Model (Hysplit) is used to study the pollutant concentrations from airborne releases in the Mississippi Gulf coast region. High resolution meteorological simulations are conducted using WRF model for typical summer scenario. The temporal and spatial variations of the meteorological fields under land-sea breeze circulations are simulated with the WRF model for a typical summer condition. The dispersion characteristics of plumes emitted from four major elevated point sources are then evaluated using the Hysplit model i) by computing the trajectories and ii) by computing the 2-h average ground-level concentrations. Estimates of ground-level concentrations of a few pollutants (SO2, NOX and CO) under complex meso-scale circulation patterns are presented.

Simulated concentrations are compared with available ambient measurements and with those obtained from a modified Gaussian Plume Model incorporating the fumigation effects. The plume trajectory and the concentration distribution are found to vary diurnally with the local land-sea breeze circulation and associated mixing height variations. Ground level concentrations are found significantly higher during the stable atmospheric conditions and the highly mixing shallow boundary layer (internal boundary layer) formation associated with sea breeze circulation. The study illustrates the complexity of the dispersion patterns which can occur for travel distances on the order of 100 km in the coastal region due to the coastal circulations and the associated boundary layer mixing.