Modeling impacts of mesoscale vertical motions upon coastal zone air pollution dispersion

This paper summarizes recent speculations on the impact of organized mesoscale vertical motions upon pollutant dispersion near coastlines. Coastal zone phenomena, previously described from limited observations and simple models are revisited using advanced meteorological and dispersion models. A prognostic mesoscale meteorological model, when combined with a Lagrangian particle dispersion model, should more realistically simulate mesoscale dispersion than conventional Gaussian-plume models in regions having strong vertical ascent and subsidence as well as wind shears, spatially variable mixing depths and recirculating wind fields. The fumigation of elevated plumes during onshore gradient flow is found to be influenced by even weak subsidence. Very fine mesh, three-dimensional simulations of sea breezes along; both straight and complex shorelines suggest that sustained mesoscale frontal updrafts may be stronger than previously suspected, at times peaking in excess of 2 ms−1. Plumes released along the shoreline can be vertically translocated almost entirely out of the sea breeze inflow layer at the front. The hypothesis that plume trajectories tend to follow mesoscale, quasi-helical patterns is supported, but it is found that plume dispersion can at times be even more complex. Within sea breeze return flows, recirculating plumes may bifurcate into distinct branches with varying amounts of pollutants subsequently entrained back into the inflow layer. The numerical simulations suggest that for plumes containing aerosols with a broad spectrum of terminal velocities, vertical motions strongly influence size sorting, resulting in complex surface concentration and deposition patterns. These results are relevant both for routine air quality dispersion and emergency response modeling. Affordable, high-performance workstations now make such models practical for many research and some real-time forecasting applications.