Impact of Topographic Circulations on the Transport and Dispersion of Air Pollutants

摘要

A numerical mesoscale model is utilized to examine slope flows and the classic mountain-plain circulation for idealized topography. Special emphasis is given to turbulent parameterization in the stable boundary layer and the unique characteristics of turbulent mixing in the slope flows. The numerical simulations for idealized valley-plain configurations produced results consistent with observations such as shallow sidewall flows, the pooling of cool air in the valley, and a deep mountain flow out of the valley. A Lagrangian particle model, operating in the terrain following coordinate system of the mesoscale model, was developed to examine pollutant transport in the modeled circulations while a Markov statistical process was used to evaluate turbulent dispersion. Higher order turbulence parameters needed for the statistical model were directly computed from the numerical model. Results of dispersion tests in the modeled slope flows showed enhanced vertical dispersion in the slope flows compared to flow over a flat boundary, and, importantly, that normal surface scaling parameters for pollutant dispersion such as friction velocity were inappropriate for the slope flows.