An improved method for charging ultrafine particles in coronas (e.g., unipolar or bipolar corona discharges) by exposing the particles to X-ray irradiation. Experimental tests have verified that positive corona in the presence of X-ray irradiation results in maximum or optimum charging efficiency, followed by a negative corona in the presence of X-ray irradiation, X-ray radiation only (without corona), negative corona only (without X-ray irradiation), and finally positive corona only (without X-ray irradiation). This method and system is particularly well suited for use with bioaerosol particles wherein exposure to the corona discharge and X-ray irradiation serves to both capture and inactivate the bioaerosol particles using a single device.