The influence of the lateral boundaries and background concentrations on limited area photochemical model simulations

In this study an attempt was made to investigate the influence of the later al boundaries and the background concentrations, on the predicted air pollu tants' concentrations, as calculated by limited area, grid-based photo-chem ical models. This influence is more pronounced in the case of mesoscale app lications because of the limited domain. The lateral boundaries should be d efined in such a way as to take into account the recirculation phenomena wh ich occur as a result of the interaction of different scale atmospheric cir culations. In addition, the influence of air pollutant sources located near the domain boundaries (inside or outside), on the concentrations of the ph otochemical pollutants inside the domain have to be considered. In this stu dy the UAM-IV photochemical model has been implemented and simulations have been performed over the Athens Basin. It was found that the concentrations of the photochemical oxidants are mainly affected by the lateral boundary conditions, while the influence of the background is evident in the first h ours of the simulation.