Atmospheric aerosols have been implicated in human health effects, visibility reduction in urban and regional
areas, acidic deposition, and altering the earth’s radiation balance. A major goal of scientific research
for the last fifteen years has been the development of the necessary models, using first principles,
that can be used in order to predict the size and composition of atmospheric particulate matter. A number
of such models assume that atmospheric aerosols are at thermodynamic equilibrium with the corresponding
gases, and they predict the chemical composition of atmospheric aerosols, using thermodynamic arguments.
The current state of the art of thermodynamic equilibrium models is reviewed in this paper, and the theory used is presented.