INSTRUMENT FOR MEASURING AND CLASSIFYING NANOMETER AEROSOLS

摘要

An apparatus (16) for classifying polydisperse aerosols includes aerosol and sheath gas conduits for conducting a sample aerosol and a sheath gas toward a merger area. At the merger area the sheath gas and about ten percent of the sample aerosol merge, then travel through a differential mobility analyzer (DMA) (24) and along a tubular electrode (62) of the DMA (24). Selected particles, i.e. particles having electrical mobilities within a narrow range, pass through a collection aperture (64) of the electrode (62). The DMA output, an aerosol consisting of the selected particles, is provided to a condensation particle counter (36) or other device for determining the aerosol concentration. The remainder of the sample aerosol is conducted away from the merger area along a bypass flow conduit (28). The bypass flow and an improved aerodynamic design provide for a slit (90) at the merger area that is sufficiently narrow to minimize unwanted electric field penetration at the slit (90) and DMA entrance (92). An annular flow restriction feature (88) in the bypass conduit (28) promotes and maintains laminar, uniform-velocity flow near the slit (90). The collection aperture (64) is located medially along the tubular electrode (62), to prevent electrical field fringing near the aperture (64).