On the basis of the Canadian Regional Climate Model (CRCM) a new regional oxidant model has been developed to study ozone climatology in eastern Canada. In addition to the semi-Lagrangian advection and vertical diffusion schemes already present for tracers, a chemical module, dry deposition parameterization, and anthropogenic and on-line biogenic emissions were added to the CRCM. The complete model forms a single system which integrates meteorological and chemical variables simultaneously. Transport of 25 chemical species is evaluated on a 80¿80 horizontal grid at 42.3 km resolution and for the 24 unequally spaced levels. The chemical scheme includes 47 species and 114 reactions used in the Acid Deposition and Oxidant Model (ADOM) gas-phase mechanism. Precalculated photolysis rates, corrected for the model cloud cover through the variations of the simulated solar radiation penetration, are used in the model. This limited-area model is driven at its boundaries by objective reanalyses for the meteorological fields and by climatological concentrations for the chemical counterparts. A time step of 15 min common to all processes is currently used. A two-step validation procedure, which 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 during 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 was substantially improved by the addition of the biogenic emission parameterization. Climatology-specific results are presented in the companion paper by Bouchet et al. . ¿ 1999 American Geophysical Union