Studying ozone climatology with a regional climate model 1. Model description and evaluation

On the basis of the Canadian Regional Climate Model. (CRCM) a new regional oxidant model has been developed to study ozone climatology in eastern Cana da. In addition to the semi-Lagrangian advection and vertical diffusion sch emes already present for tracers, a chemical module, dry deposition paramet erization, and anthropogenic and on-line biogenic emissions were added to t he CRCM. The complete model forms a single system which integrates meteorol ogical and chemical variables simultaneously. Transport of 25 chemical spec ies is evaluated on a 80 x 80 horizontal grid at 42.3 km resolution and for the 24 unequally spaced levels. The chemical scheme includes 47 species an d 114 reactions used in the Acid Deposition and Oxidant Model (ADOM) gas-ph ase mechanism. Precalculated photolysis rates, corrected for the model clou d cover through the variations of the simulated solar radiation penetration , are used in the model. This limited-area model is driven at its boundarie s by objective reanalyses for the meteorological fields and by climatologic al concentrations for the chemical counterparts. A time step of 15 min comm on to all processes is currently used. A two-step validation procedure, whi ch includes specific cases and climatological simulations, was adopted. The first test consists of a week-long simulation for the first week of August 1988 when an intense ozone episode affected most of northeastern America d uring the first Eulerian Model Evaluation and Field Study (EMEFS) campaign. Results show that the CRCM ability to simulate this episode is comparable to other existing models using off-line approaches. The CRCM performance wa s substantially improved by the addition of the biogenic emission parameter ization. Climatology-specific results are presented in the companion paper by Bouchet et al. [this issue].