A cloud microphysics model including trace gas condensation and sulfate chemistry

A one-dimensional model for simulating the evolution of physical and chemical properties of an aerosol population has been developed in order to simulate cloud or fog droplet formation. The physicochemical processes affecting the aerosol population and included in the model are condensation and evaporation of water vapor and trace gases, gas emissions, and reversible and irreversible chemical reactions producing sulfate in the liquid phase. The model also includes modules for equilibrating the aerosol population with water vapor and trace gases, and for calculating the optical properties of the aerosol population. In this article, we compare the model results with other cloud models, and show that very similar fractions of activated particles are obtained using the thermodynamical models EQUISOLV II and AIM. We point out that when ammonia and strong acids (nitric and/or hydrochloric) are present in the system, the methods for the initial equilibration of the semi-volatile compounds can have a significant effect on the simulation results. We also compare the effects of nitric and hydrochloric acid with cloud drop activation and study sulfate production in the presence and in the absence of condensable trace gases.