The CALGRID mesoscale photochemical grid model—I. Model formulation

Abstract A new photochemical oxidant model, CALGRID, has been developed for regulatory assessments of ozone control strategies. The model features: low numerical diffusion transport schemes that explicitly conserve mass on a terrain following mesh; modern boundary-layer representations converted to K-theory and applied to a variety of both fixed level and space-time variable vertical meshes; the ability to switch chemical schemes easily among the SAPRC hierarchy; a comprehensive resistance-based, dry deposition algorithm; and a highly-modular, streamlined FORTRAN 77 code that is highly vectorized and easily adapted to emerging parallel processor technology. The model is controlled by an easy to modify, self-documenting “control file” which also enables many consistency checks and serves to protect against a number of simple, yet common, simulation errors. The paper describes each of the model's principal technical modules in detail.