Accurate Determination Of Mass And Diameter Of Monodisperse Particles By The Electro-Gravitational Aerosol Balance: Correction For The Work Function Imbalance Between The Electrode Surfaces

The electro-gravitational aerosol balance (EAB) is a method of measuring the mass of nearly monodisperse aerosol particles using a Millikan-type cell. We propose in the present study a procedure for evaluating and correcting for the work function imbalance between the opposing electrode surfaces of the EAB cell, which might produce a bias in the mass measurement. In this procedure, EAB measurement is conducted for the same particles in multiple configurations in which the EAB cell is inverted and/or the electrical polarity of the particles is reversed. The differences between the apparent masses obtained in the multiple configurations are used to evaluate the work function imbalance. This procedure was applied to 100 nm and 300 nm polystyrene latex particles. The work function imbalance was found to be 34.5 meV +/- 3.8 meV (the number following the symbol +/- indicates the expanded uncertainty with a coverage factor of 2), which, if not corrected for, would lead to a measurement bias of approximately 9.6% in terms of mass, or 3.2% in terms of diameter, of the 100 nm particles, an effect that cannot be left uncorrected for. The number average mass and diameter of the 100 nm particles after correction for the work function imbalance were 585.7 ag +/- 6.3 ag and 101.71 nm +/- 0.39 nm, respectively. The small uncertainties show that the EAB method with the procedure of correcting for the work function imbalance is suited to developing particle mass and size standards. It was also confirmed that the difference in mass between positively charged particles and negatively charged particles was negligibly small. The effect of the work function imbalance on measurement of the 300 nm particles was not significant. Copyright (c) 2020 American Association for Aerosol Research