Technical note: Measurement of chemically resolved volume equivalent diameter and effective density of particles by AAC-SPAMS

Abstract

Size and effective density (ρe) are important properties of aerosol particles and are related to their influences on human health and the global climate. The volume equivalent diameter (Dve) is an intrinsic property that is used to evaluate particle size. Three definitions of ρe are generally used to characterize the physical property of a particle as an alternative to particle density, in which only the ρeII, defined as the ratio of particle density (ρp) to a dynamic shape factor (χ), has the characteristic of being independent of particle size. However, it is still challenging to simultaneously characterize the Dve and ρeII of aspherical particles. Here, we present a novel system that classifies particles with their aerodynamic diameter (Da) by aerodynamic aerosol classifier (AAC) and determines their vacuum aerodynamic diameter (Dva) by single-particle aerosol mass spectrometry (SPAMS) to achieve a measurement of Dve and ρeII. The reliability of the AAC-SPAMS system for accurately obtaining Dve and ρeII is verified based on the result that the deviation between the measured and theoretical values is less than 6 % for the size-resolved spherical polystyrene latex (PSL). The AAC-SPAMS system was applied to characterize the Dve and ρeII of (NH4)2SO4 and NaNO3 particles, suggesting that these particles are aspherical and their ρeII is independent of particle size. Finally, the AAC-SPAMS system was deployed in a field measurement, showing that it is a powerful technique to characterize the chemically resolved Dve and ρeII of particles in real time.