A system for measuring size segregated mass concentration of an aerosol. The system includes an electromagnetic radiation source with beam-shaping optics for generation of a beam of electromagnetic radiation, an inlet sample conditioner with adjustable cut-size that selects particles of a specific size range, and an inlet nozzle for passage of an aerosol flow stream. The aerosol flow stream contains particles intersecting the beam of electromagnetic radiation to define an interrogation volume, and scatters the electromagnetic radiation from the interrogation volume. The system also includes a detector for detection of the scattered electromagnetic radiation an integrated signal conditioner coupled to the detector and generating a photometric output, and a processor coupled with the conditioner for conversion of the photometric output and cut-size to a size segregated mass distribution.