The Modal Aerosol Dynamics (MAD) model is a computationally efficient model for solving the General Dynamics Equation of Aerosols (GDE) (Friedlander, 1977). The simplifying assumption in the model is that aerosol size distributions can be approximated by overlapping modes, each represented by a continuous analytical distribution function. The development of the model for atmospheric aerosols makes use of log-normal distribution functions (LNDFs), because they reasonably represent experimental data (Whitby, 1978). The paper describes the solution of the coagulation and gas-to-particle conversion (without nucleation) terms of the GDE using the MAD model.