The cloud settling effect for aerosol particles is examined based on approximation of long-range particle-particle hydrodynamic interactions. It is indicated that the normalized cloud settling velocity (CSV) exhibits a linear relationship with the product of particle number and particle size ratio. A particle-level analysis, combined with the Stokes/Oseen dynamics simulation, is applied to study the effects of fluid inertia and cloud shape on the CSV. Prediction functions for both spherical and columnar clouds, considering the effect of fluid inertia, are obtained through both simulation regression and analytical derivation. (C) 2015 Elsevier Ltd. All rights reserved.