A numerical method for calculating the ion- and particle-charge density, the electric field intensity, and, consequently, the ion- and particle-current density in a wire-duct electrostatic precipitator is reported. This method is based on numerically solving the main set of equations defining the ionized field. These include Poisson's equation, the current density equation, and the current continuity equation. The space-charge-free field is calculated using the charge simulation technique. The distribution of the electrical conditions is determined as a function of the applied voltage. Both cement and steel particles are considered. This method is checked against published calculations. Findings are correlated to the physics of corona discharge.