Development and Application of New Modeling Techniques for Mesoscale Atmospheric Chemistry

New modeling techniques have been developed to improve the capabilities of the Regional Acid Deposition Model (RADM). Grid resolution has been increased both horizontally, through the development of a nested grid version of RADM, and vertically by increasing the number of vertical layers from 6 to 15. In addition, a new algorithm for subgrid vertical transport in the convective boundary layer (CBL) has been developed to take advantage of the more detailed vertical grid structure. The resulting refined model is then used in conjunction with vertically resolved aircraft measurements to investigate the relationships between vertical chemical distributions and the dynamical and thermodynamical structure of the lower troposphere. Finally, both observed and modeled data are used to examine the interactions between chemical processes and dynamical processes, such as vertical mixing, plume dilution, and advection. A nested grid version of RADM, using a 1/3 horizontal grid cell size or 80/3 = 26.7 km, has been developed so that increased resolution can be applied to critical areas while retaining influence of larger scale phenomena. Comparisons to the fourth experiment of the Oxidant and Scavenging Characteristics of April Rains (OSCAR IV) show more realistic simulation of the dynamic range of wet deposition amounts by the nested model than by the coarse grid model. Comparisons to the high density sampling net network (110 x 110 km) indicate that the nested model is able to simulate features on a scale which is subgrid to the coarse grid model. A new algorithm for subgrid vertical transport of trace chemical material in the convective boundary layer has been developed. The new model, named the Asymmetrical Convective Model, is a simple non-local closure model designed to simulate the asymmetrical nature of upward and downward transport in the CBL. Tests of the ACM show it to be superior to eddy diffusion models and other simple non-local closure models (i.e. Blackadar, 1978) in simulating subgrid vertical transport from sources at any level above, below or within the CBL. Analysis of nested and aircraft data show the influence of boundary layer structure on chemical distributions. Examination of the interactions between various chemical and physical processes show that vertical mixing within the CBL can systematically alter chemical equilibrium states. The aircraft data indicates that chemical equilibrium can also be disturbed by concentrated plumes mixing into cleaner background air.