The Coastal Aerosol Transport (CAT) model was developed to study the evolution of aerosol particle size distributions and composition in the coastal environment. The model simulates such processes as particle production at the sea surface, mixing of particles through the boundary layer by turbulent diffusion, gravitational settling, and dry deposition. The model is initialized at the shoreline with continental and/or surf aerosol. An empirical source function was developed which better accounts for the production of submicron particles than current formulations. Continental and sea spray particles are treated separately to account for effects of processes depending on chemical composition. CAT has been tested by comparison with independent data sets as regards the prediction of particle size distributions, the wind speed dependence of sea-salt aerosol mass concentrations, and the evolution of sea spray aerosol plumes generated over the surf zone. The model was applied to study effects of sea spray aerosol produced in the surf zone on sea spray concentrations, the composition of continental/sea spray aerosol mixture, the uptake of nitric acid by sea spray aerosol, and the effect of the latter process on nitric acid profiles. The results lead to the conclusion that surf-produced aerosol cannot be neglected in studies of processes involving sea spray aerosol in the coastal atmospheric boundary layer. ¿ 2001 American Geophysical Union