In this paper, a modified numerical method for calculating the electrical conditions, namely the charge density, the electric field intensity and the current density, in wire-duct electrostatic precipitators is reported. Variation of mobility for both ions and particles in the space surrounding the energized wires is taken into consideration. This method is based on numerically solving the main set of equations, defining the ionized field with presence of dust particles. The space-chargefree field is calculated using the charge simulation technique. This method is checked against published calculated and measured results, showing good agreement. The present findings are correlated to the physics of electrical corona discharge.