Radial differential mobility analyzer

The present invention provides a differential mobility analyzer for the classification of aerosols, comprising a chamber having two generally parallel faces and means to confine gases in the chamber, one of the faces having a generally arcuate, annular sheath air channel having an axis of symmetry, other of the faces having a generally arcuate, annular aerosol channel having an axis of symmetry generally coincident with the axis of symmetry of the sheath air channel, a first one of the faces having a sample flow aperture generally aligned with the axis of symmetry of the sheath air channel, a second one of the faces having an excess flow aperture generally aligned with the axis of symmetry of the sheath air channel, and means for maintaining an electric potential difference between the faces.