Using an inkjet aerosol generator to study particle bounce in optical particle counters

Abstract

The overall counting performance of two optical particle counters (OPCs), which had a sampling flowrate of 28.3 L/min, was evaluated. An inkjet aerosol generator (IAG) was used to generate at a constant rate monodisperse test particles in the size range of 0.3–10 µm. The effect of particle phase on the counting efficiency (CE) of the two OPCs (RION KC-31 and Lighthouse Solair 1100) was characterized. Lactose monohydrate (LM) and sodium chloride (NaCl) particles were used as the solid particles. The particles of a water-soluble ionic liquid were used as the liquid particles. The CEs were evaluated for polystyrene latex (PSL) particles using a parallel comparison method. The CE of each of the two OPCs measured for solid particles was different from that measured for liquid particles. With liquid particles, the CE decreased over the micrometer range indicating that the particles had deposited on a surface within the OPC. Each CE had a sharp minimum for LM particles when the aerodynamic diameter of the particles, (Formula presented.) was in the 2.5–2.6 µm range. The probability of particle bounce was evaluated using other experiments, and the results suggested that solid particles whose (Formula presented.) was in the 2.6–2.9 µm range would bounce off at the inner surface of the focusing segment of the OPC, located upstream of the optical system. The CEs measured when using NaCl and PSL particles were close to unity and did not decrease over a few micrometer range; however, these particles also would bounce off. Copyright © 2021 American Association for Aerosol Research.