Description of the evolution of the size and chemical composition of aerosols in plumes is fundamental to the ability to predict visibility impairment. Previously, it has only been possible to predict changes in aerosol size distributions in plumes. In this work the first model for predicting both size and chemical composition evolution of plume aerosols is presented. Coagulation, homogeneous particle formation, heterogeneous condensation, and particle phase chemical equilibria and kinetics are explicitly included. The model is based on a sectional representation of the size-composition spectrum and computation is easy to implement. This model holds promise to be a standard component of all plume visibility calculations that require plume aerosol size and composition information.