An approach to evaluating and correcting aerodynamic particle sizer measurements for phantom particle count creation.
Am Ind Hyg Assoc J 1992 Jul; 53(7):427-431
A method was presented for correcting aerodynamic particle sizer (APS) data for phantom particle creation. In measurements made by the APS, particle size is determined by the time it takes a particle to travel between two laser beams which are fixed perpendicular to an accelerating airflow. On the occasions where only a single pulse is detected from a particle, another pulse can cause the recording of a randomly sized phantom particle. Phantom particles can be created by the small particle processor (SPP) which was developed to determine particle transit times in digital increments of 4 nanoseconds. The creation of phantom particles is prevented in the large particle processor (LPP) which determines the travel time in digital increments of 66.67 nanoseconds. In the range of 5.2 to 15.4 micrometers, these two processors overlap. In this method an estimate of the upper limit of the number of phantom particles in each data channel from the SPP can be calculated using the difference in particle counts in this overlap region. Since the large particle processor of the aerodynamic particle sizer responds to coincidence by underestimating the concentration of particulate matter in the aerosol, it is important for the user to exercise some caution in interpreting the results. The data is not purified of the statistical noise caused by phantom particle creation by using this method for correction.
NIOSH-Author; Aerosols; Aerosol-particles; Aerosol-sampling; Air-quality-monitoring; Airborne-particles; Measurement-equipment;
American Industrial Hygiene Association Journal