A New Technique to Calibrate Optical Particle Counters Aerodynamically

Abstract

The calibration curve of an optical particle counter (OPC) normally is established based on the relationship between the optical responses of spherical particles (e.g., polystyrene latex spheres) and the particle sizes. This calibration curve, however, cannot be used to size unknown aerosol particles accurately in the field. A new technique was developed that allowed calibration of OPCs by using aerosol particles that the instruments will be measuring. A two-stage virtual impactor was used to classify aerodynamically monodisperse aerosols of fly ash, oil shale, triphenyl phosphate, tale, glass microspheres, and alumina for calibrations of a Royco 226 OPC. Particles with the same aerodynamic diameter produced optical responses in the OPC that depended not only on the geometric size but on the refractive index, density, and morphology. Calibration curves of test aerosols, except that of the triphenyl phosphate, were different from that of polystyrene latex spheres. The results indicated that OPCs can be calibrated accurately for field aerosols by using a two-stage virtual impactor as a sampling inlet and, thus, OPC applications can be enhanced greatly.