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

Abstract. Size and effective density (ρ_e) are important properties of aerosol particles and are related to their influences on human health and the global climate. The volume equivalent diameter (D_ve) is an intrinsic property that is used to evaluate particle size. ρ_e, defined as the ratio of particle density to a dynamic shape factor (χ), is used to characterize the physical property of a particle as an alternative to particle density. However, it is still challenging to simultaneously characterize the D_ve and ρ_e of particles. Here, we present a novel system that classifying particles with their aerodynamic diameter (D_a) by aerodynamic aerosol classifiers (AAC) and determining their vacuum aerodynamic diameter (D_va) by single particle aerosol mass spectrometry (SPAMS) to achieve a measurement of D_ve and ρ_e. The reliability of the AAC-SPAMS system for accurately obtaining D_ve and ρ_e is verified based on the results that the deviation between the measured values and the theoretical values is less than 4 % for the size-resolved spherical polystyrene latex (PSL). The AAC-SPAMS system is applied to characterize the D_ve and ρ_e of (NH₄)₂SO₄ and NaNO₃ particles, suggesting that these particles are aspherical and their ρ_e are independent of particle size. Finally, the AAC-SPAMS system is deployed in a field measurement, showing that it is a powerful technique to characterize the chemically-resolved D_ve and ρ_e of particles in real time.