Abstract: In this work we present a model, CAPAS, capable of estimating short-term concentrations of primary and secondary pollutants resulting from point source emissions.  The model is designed to simulate the complex interaction of plume dispersion and non-linear chemistry.  The main features of the model are: (1) the horizontal and vertical resolution within the plume, which offers a realistic treatment of the entrainment process, (2) its flexibility with regard to choices of chemical kinetic mechanism, and (3) its simplicity of operation and adaptability to solve new problems.