Abstract: An inertial impactor with a specially designed impaction plate has a nozzle protruding from a nozzle plate, and an impaction plate formed with a conical recess covered by an orifice plate and a circular impaction plane at the bottom of the recess having a diameter slightly greater than that of the diameter of the nozzle. The impactor reduces loss of particles due to rebounding or blowing off particles from the impaction plate so as to increase particle collection efficiency and capacity, permit a quick accumulation of the particles on the bottom of the conical recess, and increase collection efficiency accordingly.