A more advanced land-surface/PBL model is implemented in the Penn State/NCAR Mesoscale Model Version 4(MM4) which is utilized to provide meteorological data to the Regional Acid Deposition Model (RADM). The diurnal evolution of the planetary boundary layer (PBL) and its dynamic characteristics are crucial to air quality modeling. The PBL is strongly dependent on surface fluxes of heat, moisture, and momentum. These fluxes are largely controlled by soil moisture and vegetative evapotranspiration. Previously, the MM4 was unable to respond to dynamic soil moisture conditions, leading to unrealistic partitioning of the surface energy budget between sensible and latent heat fluxes. The new model includes explicit soil moisture and evapotranspiration, as well as improved radiation and cloud cover algorithms, flux-profile relationships, and PBL mixing. The soil-vegetation-atmosphere transfer scheme is similar to the scheme developed for the French Weather Service mesoscale meteorological model. The PBL mixing scheme, a hybrid of eddy diffusion and nonlocal closure, is the same as is currently used in the RADM. The model has been previously tested in 1-D form against several field experiments and has demonstrated good agreement with measurements.