Coagulation of aerosols involving electrostatic and van der Waals forces together with Brownian force was studied for the cases of monodisperse and polydisperse aerosols. Using histogram size distribution for particles, the coagulation rate of the combined aerosol was investigated. A simplified model was used by introducing the aerosol size distribution functions instead of two individual spherical particles, to study the electrostatic coagulation effect. Numerical methods were employed to calculate the integral equation to determine the coagulation rate. Using this method and assuming that the charge is uniformly distributed for a given size band, the lower and upper limits of charge, within which the electrostatic forces become dominant, has been identified. In addition, the concentration of particles with coagulation time was examined by solving the dynamic equation for charged particles.