Updating applied diffusion models.

Abstract

Most diffusion models currently used in air quality applications are substantially out of date with understanding of turbulence and diffusion in the planetary boundary layer. Under a Co-operative Agreement with the Environmental Protection Agency, the American Meteorological Society organized a workshop to help improve the basis of such models, their physics and hopefully their performance. Reviews and recommendations were made on models in three areas: diffusion in the convective boundary layer (CBL),diffusion in the stable boundary layer (SBL) and model uncertainty. Progress has been made in all areas, but it is most significant and ready for application to practical models in the case of the CBL. This has resulted from a clear understanding of the vertical structure and diffusion in the CBL, as demonstrated by laboratory experiments, numerical simulations, and field observations. All of these investigations have shown the importance of the convective scaling parameters: w*, the convective velocity scale and zi, the CBL height. This knowledge and the non-Gaussian nature of vertical diffusion have already been incorporated in some applied models and show much promise. The workshop has made a number of recommendations concerning the use of this information.-from Author