SMPS and DMA Calibration with Size-Certified Silver Aerosols from the Silver Particle Generator (SPG)
Tobias Hammer, MOHSEN KAZEMIMANESH, Hans-Joachim Schulz, Konstantina Vasilatou, National Physical Laboratory
Abstract Number: 316
Working Group: Instrumentation and Methods
Abstract
Scanning mobility particle sizers (SMPS), consisting of differential mobility analyzers (DMAs) and condensation particle counters (CPCs), should be regularly calibrated using size-certified particles in the sub-micrometer range. Previous study has shown that the silver particle generator (SPG, Catalytic Instruments) can generate silver particles with a mobility diameter down to ~5 nm in a stable manner. In this study, we characterize the commercially available SPG and evaluate its applicability for calibrations of DMAs and of entire SMPS systems. Different makes and models of SMPS / DMA were calibrated in the measurement campaign.
The arithmetic mean, geometric mean, and mode mobility diameters of the aerosols from two setpoints (setpoint 1 and 2 with a GMDmob of 10 nm and 25 nm, respectively) were compared to the average geometric diameters determined by a size-traceable transmission electron microscope (TEM). The collected particles from both setpoints were analyzed for Feret diameter, projected area diameter, aspect ratio, and circularity using TEM image analysis. This comparison revealed a maximum offset between DMA and TEM of 0.8 ± 0.2 nm (i.e., ± 8% of nominal size) for the setpoint 1 when considering particle Feret diameter. The projected area diameter was slightly smaller and a greater offset of 1.2 ± 0.3 nm existed between DMA and TEM. For the setpoint 2, the maximum offset between DMA and TEM was 4.1 ± 0.5 nm off-set when considering Feret diameter, while this offset was larger when comparing to project area diameter of particles. The smaller offset observed for setpoint 1 is presumably due to nearly spherical particles produced in this setpoint (where their geometric and mobility diameters are similar), whereas we observed a mix of spherical and agglomerate particles in setpoint 2. These differences should be accounted for when calibrating SMPS and DMA.