A Combined Modelling System for the Simulation of the Transport and Dispersion in Coastal Areas

Abstract

Mesoscale circulations and local effects caused by coastlines and orographic relief exert a significant influence on the structure of the atmospheric boundary layer and consequently on transport and dispersion of pollutants, which can be rarely described by simplified models. Most regulatory dispersion models are based on the steady-state Gaussian plume approach which assumes that flow is stationary and homogeneous. These hypotheses are no longer valid in presence of complex circulations. In such cases the ground-level impact of plumes is often determined by non-stationary 3 dimensional trajectories, which should be computed and used to drive pollutant transport and dispersion calculations. Here, a combined approach to air pollution modelling in complex terrain is presented. The systems couples RAMS (Regional Air Meteorological System, Boulder Co, US, Pielke et al. 1992), a nonhydrostatic mesoscale model, CALMET (Scire et al. 1990), a 3D diagnostic model and a Lagrangian puff dispersion model, CALPUFF, (Scire et al. 1990b). In this way the wind field generated by RAMS is able to resolve both mesoscale circulations and local circulation systems generated by land-sea temperature gradients. CALMET provides the three-dimensional wind and temperature fields, and two-dimensional fields of boundary layer parameters to be used by the Lagrangian puff dispersion model CALPUFF.