A geometrical sintering model (GSM) to predict the surface area variation with time is proposed. Predictions of the GSM are compared to the commonly used Koch and Friedlander [(1990). The effect of particle coalescence on the surface-area of a coagulating aerosol. Journal of Colloid and Interface Science, 140, 419-4271 model, mass transport based viscous flow sintering models and to experimental data reported in the literature. Closed form expressions for the normalized surface area variation with time are derived for specific sintering mechanisms such as overall diffusion and viscous flow. For other sintering mechanisms such as surface, grain boundary, and volume diffusion, closed form expressions could be derived by making simplifying assumptions of a reference radius for the primary particles. (c) 2005 Elsevier Ltd. All rights reserved.