Continued Research in Mesoscale Air Pollution Simulation Modeling. Volume 6. Further Studies in the Modeling of Microscale Phenomena

摘要

This report describes the development of techniques for modeling the microscale phenomena associated with urban air pollution. Such phenomena include turbulent diffusion, turbulent concentration fluctuations, and sub-grid scale variations in the time averaged concentration field. Optimal eddy diffusivities were reexamined to determine whether (1) the diffusivities are unique, (2) they have a universal form when properly scaled, and (3) they are dependent on source height. A model for describing the effects of turbulent concentration fluctuations on second-order chemical reactions has also been developed and tested. It was applied to the case of NO emanating from a point source into an O3 laden atmosphere. Results showed that the rate of conversion of NO to NO2 is greatly inhibited by turbulent concentration fluctuations, even under stable conditions. A method of paramaterizing the effects of chemical reaction rates of both subgrid-scale concentration variations arising from ground-level sources and turbulence-induced concentration fluctuations has also been developed. In addition, theoretical frameworks for two models of pollutant levels around roadways are introduced.