Fernández-Díaz and Domat's preceeding Letter to the Editor argued that the geometry of the discharge electrode of the charger of our previous article entitled "Modeling and Validation of Nanoparticle Charging Efficiency of a Single-Wire Corona Unipolar Charger" was a needle but not a wire. Therefore, the boundary condition for the ionic charge density at the discharge wire surface used in the simulation was suspected to be not completely correct. In the present work, the exact shape of the tip of the discharge electrode was examined and found as a hyperbolic point. The experimental onset voltage was further compared with the theoretical onset values calculated by either wire-in-tube or point-to-plane assumption. Results show that the theory of needle-type discharge electrode is also not appropriate either for the boundary condition at the tip because of higher calculated onset voltages than the experimental data.