The atmospheric flow and pollutant dispersion over the Po plains in high-pressure conditions and weak synoptic circulation is investigated by means of a model simulation. This study stems from the work conducted during the Pianura Padana Production of Ozone (PIPAPO) campaign conducted in 1998. The typical mesoscale flow that establishes in the Po plains under these conditions is responsible for the diffusion of atmospheric pollutants in the prealpine valleys, their recirculation over the plain, and in general for the condition of stagnation and pollution buildup often found in the region. The model simulation presented here reproduces correctly the meteorological circulation that occurred in the central part of the Po valley during the PIPAPO first intensive observational period. The model results are compared with the measurements collected at a large number of surface observational sites and the airborne instruments deployed during the campaign. Subsequently, the diffusion and transformation process of the atmospheric pollutants is analyzed. Direct comparison with the measurements collected during the campaign indicates the good quality of the model results and the relevance of the conclusions deduced from the model simulation. This paper represents one of the few attempts made so far to simulate the circulation and photochemical ozone production over the Po plains.