Simulation of aerosol dynamics: A comparative review of algorithms used inair quality models

A comparative review of algorithms currently used in air quality models to simulate aerosol dynamics is presented, This review addresses coagulation, condensational growth, nucleation, and gas/particle mass transfer, Two majo r approaches are used in air quality models to represent the particle size distribution: (1) the sectional approach in which the size distribution is discretized into sections and particle properties are assumed to be constan t over particle size sections and (2) the modal approach in which the size distribution is approximated by several modes and particle properties are a ssumed to be uniform in each mode. The sectional approach is accurate for c oagulation and can reproduce the major characteristics of the evolution of the particle size distribution for condensational growth with the moving-ce nter and hybrid algorithms, For coagulation and condensational growth, the modal approach provides more accurate results when the standard deviations of the modes are allowed to vary than it does when they are fixed. Predicti ons of H2SO4 nucleation rates are highly sensitive to environmental variabl es and simulation of relative rates of condensation on existing particles a nd nucleation is a preferable approach. Explicit treatment of mass transfer is recommended for cases where volatile species undergo different equilibr ium reactions in different particle size ranges (e.g., in the presence of c oarse salt particles). The results of this study provide useful information for use in selecting algorithms to simulate aerosol dynamics in air qualit y models and for improving the accuracy of existing algorithms.