An experimental approach to correcting counting errors in the aerodynamic particle sizer (APS Model 3310).
Sreenath-A; Ramachandran-G; Vincent-JH
Part Part Syst Charact 1999 Dec; 16(6):257-265
This paper describes the different ways of analyzing the output of a real-time device for measuring and counting airborne particles, the aerodynamic particle sizer (APS). This instrument is very widely used in aerosol research throughout the world. It is a time-of-flight instrument in which a particles measured transit time in the changing flow in a jet passing between two laser beams is converted to its aerodynamic diameter. As the particle passes between the two laser beams, two signal processors, the small particle processor (SPP) and the large particle processor (LPP), independently provide measures of the particles transit time from the light pulses that are produced. This information is related to the aerodynamic particle diameter of the particle (dae) by means of calibration against unit density (1000 kg/m3) spheres. If more than one particle is involved in the analysis of particle transit time, then it gives rise to coincidence effects, resulting in phantom particle generation. The SPP is known to generate phantom counts, while the LPP is known to reduce phantom counts. A new method is described in this paper that gives guidance on how to deal with such coincidence problems. The principle is that it relies on additional information to obtain correction factors. In this case, well-established theory for the aspiration efficiencies of thin-walled aerosol sampling probes has been used along with corresponding experimental data obtained in a wind tunnel using the APS. Results using this method are compared with various other methods that have been tried in the past. The paper provides insights on to how the user can operate the APS to avoid counting errors like those described, and the advantages and limitations of different correction methods are discussed.
Airborne-particles; Airborne-dusts; Airborne-fibers; Aerosols; Aerosol-particles; Aerosol-sampling; Sampling; Sampling-methods; Sampling-equipment
Gurumurthy Ramachandran, Assistant Professor, Division of Environmental and Occupational Health, School of Public Health, University of Minnesota, Minneapolis, Box 807 Mayo, 420 Delaware Street, S.E., MN 55455 (USA)
Particle and Particle Systems Characterization
University of Michigan, Ann Arbor, Michigan