Modeling of Contaminant Dispersion in Complex-Terrain Flows

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ABSTRACT CTS-9708452 FERNANDO This proposal was submitted to the environmental Geochemistry and Biochemistry (EGB) solicitation NSF 96-152. The aim of this research program is to utilize the complementary expertise of laboratory experimentalists, turbulence modelers, numerical analysts and field observationalists to carry out an interdisciplinary study of air flow and pollutant dispersion, including chemical and physical transformations, in rugged (complex) terrain. As a result of restricted vertical mixing, pooling of air during nocturnal cooling and absence of background meso-scale wind flow to flush the basins, urban developments in complex terrain are prone to severe air pollution problems. Often the important surface features which influence the local wind flows are of the order of 100 meters while the valley diurnal air motions are governed by scales of more than 100 km. These scale disparities pose a difficult problem for numerical models. In addition, during morning and evening transitions from cooling to heating of the ground and vice-versa (turnover or transitional periods), wind motions are intermittent with wind speeds of the order of one meter per second, thus posing problems for field measurements. The existing models for the prediction of flow and dispersion in these areas are known to yield unsatisfactory results, especially during turnover periods. The proposed work will be directed primarily toward the development of a robust, general-purpose, geo-chemo-physical numerical model for complex-terrain flows and its validation. Laboratory and theoretical studies will be conducted to improve the fundamental understanding of and develop new parameterizations for complex-terrain, non-equilibrium turbulent flows. Detailed analyses of particle samples taken in selected field sites at 10 minute intervals will be used for the validation of turbulence parameterizations and the development of an aerosol model. An available meteorological model will be significantly m odified to incorporate these new parameterizations, including unsteady vertical mixing and aerosol transport and chemistry. This new complex-terrain model will be tested and calibrated against available and new field data. The wind fields during transitional low-wind periods will be deduced by using properly scaled laboratory complex-terrain models; a physical model of the Phoenix, Arizona area will be used for this purpose. The numerical model will be run for specific areas -- with realistic initial and boundary conditions and source distribution -- for operational forecasting of wind fields, pollutant levels, impacts on soil, interaction between indoor and outdoor air and assessment of human exposure.