Evaluation of the Equilibrium, Dynamic, and Hybrid Aerosol Modeling Approaches in a One-Dimensional Lagrangian Trajectory Model

Abstract

Recently developed dynamic and hybrid methods are compared with the equilibrium approach in a one-dimensional Lagrangian trajectory model. The three aerosol modules are incorporated into a trajectory model which includes descriptions of gas-phase chemistry, secondary organic aerosol formation, vertical dispersion, dry deposition, and emissions. The three approaches are evaluated against results from the 1987 August Southern California Air Quality Study (SCAQS). All three models predict the PM2.5 (particulate matter with diameter equal to or less than 2.5 microns) and PM₁₀ (particulate matter with diameter equal to or less than 10 microns) mass concentrations of the major aerosol species with errors less than 30%. For the aerosol size/composition distribution, however, the dynamic and hybrid models show better agreement with measurements than the equilibrium model. The hybrid model aerosol size distribution predictions are similar quite closely to the dynamic model results, which are regarded as the most accurate. The hybrid approach in this case combines accuracy with computational efficiency. The equilibrium approach remains a viable alternative for PM_2.5 and PM₁₀ simulations. The dynamic approach is the most accurate, but at a high computational cost.