A method for parameterizing sub-grid scale aerosol dynamics of freshly emitted aerosol is developed. This approach is based on the calculation of the probability that a given particle emitted inside a computational grid cell will survive and be available for transfer outside the cell. This survival probability is calculated as a function of the emitted particle size, the preexisting aerosol size distribution and the grid-cell mean advection time scale. The approach can be used in three-dimensional chemical transport models (CTMs) of all scales, from urban to global. The parameterization's results are evaluated against the predictions of a detailed one-dimensional aerosol dynamics model under a variety of atmospheric conditions. The parameterization agrees well with the dynamic model when the mean emitted particle size is smaller than that of the existing particles. Finally, the method for applying the sub-grid coagulation parameterization to a CTM is discussed. (C) 2009 Elsevier Ltd. All rights reserved.