Model for Simulating Aerosol Interactions and Chemistry (MOSAIC)

This paper describes and evaluates a new Model for Simulating Aerosol Interactions and Chemistry (MOSAIC), with a special focus on addressing the long‐standing issues in solving the dynamic partitioning of semivolatile inorganic gases (HNO 3 , HCl, and NH 3 ) to size‐distributed atmospheric aerosol particles. The coupled ordinary differential equations (ODE) for dynamic gas‐particle mass transfer are extremely stiff, and the available numerical techniques are either very expensive or produce oscillatory solutions. These limitations are overcome in MOSAIC with a new dynamic gas‐particle partitioning module, which is coupled to an efficient and accurate thermodynamics module. The algorithm includes a new concept…