Tracking the transformation of aerosol particles that are inside cloud droplets is perhaps the most challenging and least explored issue related to cloud processing of aerosols. When consideration is limited to processing of aerosol particles (AP) with a uniform chemical composition (e. g., every AP is ammonium sulfate), one relatively straightforward approach is to treat APs and cloud droplets in a joint two-dimensional size distribution, in which the actual wet particle size/volume and the dry particle size/volume are two independent variables. Unlike other bin models, this formulation preserves the dry distribution of APs exactly during the water condensation-evaporation cycle and provides a framework for predicting changes in the AP distribution due to drop coalescence and aqueous chemistry. We introduce the new microphysics module that accounts for in-cloud transformation of AP spectrum due to condensation/evaporation, collision/coalescence, advection and turbulent mixing, and sulfate production from S(IV) oxidation, in a series of simulations using a parcel (box) model as well as a fully interactive multidimensional framework. Benefits and limitations of the approach are discussed as are various aspects of numerical implementation and accuracy of the algorithm.