Mathematical formalisms that incorporate the physical processes responsible for the vertical redistribution of a conservative pollutant tracer due to a convective cloud field are presented. Two modeling approaches are presented differing in the manner in which the cloud fields are forced. In the first or implicit approach, the vertical cloud development is limited by the satellite observed value, and cloud forcing is determined from synoptic-scale heat and moisture budgets. In the explicit approach, the vertical development is similarly limited, but the forcing functions are obtained by explicitly incorporating the vertical distribution of cumulus cloud cover, thereby dynamically incorporating the influences of sub-synoptic scale phenomena. The two approaches give internally consistent results and give similar results for the convective mass flux. The manner in which the upward mass flux is apportioned to the various cloud classes, however, differs as consequence of the different vertical profile of forcing functions used. The explicit model gave more reasonable profiles but the predictions are highly sensitive to input conditions. The implicit model was somewhat less sensitive to its input parameters if the data are prepared judiciously. This study shows that the concentration increase in the cloud-layer due to the venting action of cumulus clouds can be as, if not more important than, the in-situ production and this process should therefore be incorporated in regional-scale transport models.

EPA project officer: Jason K.S. Ching. Prepared by the Department of Atmospheric and Oceanic Science, University of Michigan, under Cooperative Agreement "January 1985." Includes bibliographical references (page 137). "EPA/600/3-85-010."