A theoretical framework for a multi-day 1000 km scale simulation model of photochemical oxidant is developed. It is structured in a highly modular form so that eventually the model can be applied through straightforward modifications to simulations of particulates, visibility and acid rain. Among the physical and chemical processes that the model is designed to handle are: horizontal transport; photochemistry and nighttime chemistry of the products and precursors of pollutant reactions; nighttime wind shear, stability stratification and turbulence 'episodes' associated with the nocturnal jet; cumulus cloud effects - venting pollutants from the mixed layer, perturbing photochemical reaction rates, etc; mesoscale vertical motion induced by terrain and horizontal divergence of the large scale flow; subgrid scale chemistry processes -- resulting from emissions from sources smaller than the model's grid can resolve; natural sources of hydrocarbons, NOx and stratospheric ozone; and others. Considerable attention is given to the question of the predictability of pollutant concentrations at long range and to the related problem of parameterization of 'mesoscale' diffusion, the design of model 'validation' experiments, and the like.

"May 1983". Includes bibliographical references. "EPA-600/3-83-035."

"A theoretical framework for a multi-day 1000 km scale simulation model of photochemical oxidant is developed. It is structured in a highly modular form so that eventually the model can be applied through straightforward modifications to simulations of particulates, visibility and acid rain. The model structure is based on phenomenological concepts and consists of 3 1/2 layers. The interface surfaces that separate the layers are functions of both space and time that respond to variations in the meteorological phenomena that each layer is intended to treat. Among the physical and chemical processes that the model is designed to handle are: horizontal transport; photochemistry and nighttime chemistry of the products and precursors of pollutant reactions; nighttime wind shear, stability stratification and turbulence "episodes" associated with the nocturnal jet; cumulus cloud effects - venting pollutants from the mixed layer, perturbing photochemical reaction rates, etc; mesoscale vertical motion induced by terrain and horizontal divergence of the large scale flow; subgrid scale chemistry processes -- resulting from emissions from sources smaller than the model's grid can resolve; natural sources of hydrocarbons, NOx and stratospheric ozone; and others. Considerable attention is given to the question of the predictability of pollutant concentrations at long range and to the related problem of parameterization of "mesoscale" diffusion, the design of model "validation" experiments, and the like.