Electric mobility spectrometer for aerosol particulates included in atmosphere to be tested

PURPOSE: To force aerosol particulates to run in axial direction so as to improve calculating accuracy as well as preventing any loss caused by adhesion thereof to the tube inside wall by providing such a device as capable of changing a selected electric mobility and an aerosol detecting apparatus. CONSTITUTION: A circular electric mobility selecting apparatus including two concentric discs 18, 20 is provided, while a first disc 18 has an annular groove 22 with its radius r1 from which a gas sample including particles to be analyzed is introduced at a flow rate q1 . A second disc 20 has an annular opening of its radius r2 (r2 >r1 ) formed across which air flow q2 passes. Between two discs and around a space 24, filtered air is injected by a flow rate q0 , and a laminar flow circulates up to a central suction tube 26 so as to suck in flow rate Q=q0 +q1 -q2 . Aerosol particles flowing across a groove with radius r2 include their mobility Z and also include such a device as being capable of changing the selected mobility Z, and an electrometer 40 functioning as a detector is provided and electrically loaded particles captured by a filter 32 induce an electric current which is measured by the electrometer 40.