The continued development of the dynamic and hybrid approaches (Pilinis et al. 2000; Capaldo et al. 2000) for the simulation of atmospheric aerosol dynamics is discussed in this paper. A linear interpolation method is proposed for the mapping of the moving aerosol size/composition distribution onto a fixed size grid. The 3 aerosol modules are incorporated into a trajectory model that includes descriptions of gas-phase chemistry, secondary organic aerosol formation, vertical dispersion, dry deposition, and emissions. The 3 approaches are evaluated against measurements from the Southern California Air Quality Study (SCAQS). All 3 models predict the 4-6 h averaged PM 2.5 (particulate matter with diameter h 2.5 microns) and PM 10 (particulate matter with diameter h 10 microns) mass concentrations of the major aerosol species with errors <30%. For the aerosol size/composition distribution, however, the dynamic and hybrid models show better agreement with measurements than the equilibrium model. The hybrid mode...