Particle Density Correction for the Aerodynamic Particle Sizer

Abstract

An analytical formula has been derived to calculate the calibration curve for particles of any given density from the calibration curve for an aerosol of a different density. The Aerodynamic Particle Sizer is based on the principle that particles accelerated from a nozzle will lag the flow, depending on their aerodynamic diameter. Because of the high flow velocity, the particle acceleration is beyond the Stokes regime, leading to a dependence on particle density. The correction formula is justified by a combination of analysis and numerical trajectory computations. The density effect is appreciable. For example, if the instrument is calibrated with unit density aerosol, 20-μm particles of density 4.0 will be oversized by 20%. The corrected calibration curves are in agreement with measurements by Baron (1984).