Direct numerical simulations of coagulating aerosols in two-dimensional, incompressible, iso-thermal mixing layers are performed. The evolution of the particle field is obtained by utilizing a moment method to approximate the aerosol general dynamic equation. We use a moment method which assumes a lognormal function for the particle size, distribution and requires the knowledge of only the first three moments. This, approach is advantageous in that the number of, equations which are solved is greatly reduced. A Damkohler number is defined to represent the ratio of convection to coagulation time scales. Simulations are performed for three flows: Damkohler numbers of 0.2, 1, and 2. The spatio-temporal evolution of the first three moments along with the mean diameter and standard deviation are discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.