Simulations of sulfate aerosol dynamics—I: Model description

A previously reported two-moment, bimodal aerosol model is extended with new parameterizations developed from a sectional model. The two moment model follows the evolution of the aerosol mass and number concentration in two modes, where each mode is characterized by a variable mass mean diameter. Sulfuric acid vapor concentration is also treated as an independent variable. The aerosol population is assumed to undergo condensational growth, coagulation, nucleation, and deposition. Parameterizations were developed for the nucleation process and to represent the transfer of mass and number from mode 1 to mode 2 as a result of condensational growth. The importance of properly simulating intermodal mass transfer is demonstrated. Comparisons of model predictions with those from sectional models of variable resolution are discussed in Part II.