Abstract: A charged particle selector having first and second circular electrical mobility selector portions is shown to include directing portions for directing particles selected by the first circular electrical mobility selector to the input of the second circular electrical mobility selector. These selectors may be combined to be in parallel instead of in series. The charged particle selector can be used to make in-line measurement of the mass and/or density of aerosol particles, to make measurements of the size of the particles and/or their distribution as well as the distribution of aerosol electrical charges.

Abstract: The invention concerns a dynamic particle mobility selector comprising two separate and parallel coaxial disks (30, 32) defining a dynamic selection zone (31), the upper disk comprising an annular slit with radius r.sub.1 and a central suction intake (38) in order to circulate a laminar, centripetal and stable air flow in the dynamic selection zone. An annular opening (36) with average radius r.sub.2 <r.sub.1 may be provided in the lower disk (32). Application to a dynamic mobility spectrometer, to a device for measuring the particle size of an aerosol and a mono-dispersed aerosol generator.