A comparative study on effective density, shape factor, and volatile mixing of non-spherical particles using tandem aerodynamic diameter, mobility diameter, and mass measurements

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A comparative study on effective density, shape factor, and volatile mixing of non-spherical particles using tandem aerodynamic diameter, mobility diameter, and mass measurements

Kazemimanesh, M; Rahman, MM; Duca, D; Johnson, TJ; Addad, A; Giannopoulos, G; Focsa, C; (2021) A comparative study on effective density, shape factor, and volatile mixing of non-spherical particles using tandem aerodynamic diameter, mobility diameter, and mass measurements. Journal of Aerosol Science , Article 105930. 10.1016/j.jaerosci.2021.105930. Green open access

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Abstract

Combustion-generated particles are typically non-spherical (soot aggregates) and sometimes mixed with organic compounds (e.g. in vehicle emissions). The effective density, dynamic shape factor, and volatile mixing of particles are widely studied using aerosol instruments that measure the particle mobility diameter, aerodynamic diameter, and mass. In theory, any of these three physical properties can be obtained from a combination of the other two. In the present study, a tandem arrangement of aerodynamic aerosol classifier (AAC; measuring aerodynamic diameter), differential mobility analyzer (DMA; measuring mobility diameter), optional catalytic stripper (CS), and centrifugal particle mass analyzer (CPMA; measuring particle mass) was used to study the effective density, dynamic shape factor, and volatile mixing of non-spherical non-homogenous particles. In terms of mass, the vast majority of the particles were purely semi-volatile mixed with soot with and without semi-volatile coating. The effective density of polydisperse non-stripped particles was relatively constant (indicating nearly spherical particles), while that of polydisperse stripped particles decreased from ∼1200 to ∼800 kg/m3 as the particle size increased (indicating a compact structure). The effective density of monodisperse particles, measured by DMA-CPMA, AAC-DMA, and AAC-CPMA methods, was consistent within the measurement uncertainty; however, the latter method had larger discrepancy with the other two methods, particularly for non-spherical particles. The dynamic shape factor, measured by AAC-CPMA and DMA-CPMA methods, increased with the mobility diameter, a trend also supported by electron micrographs. The volatile mass fraction of particles decreased as their mobility diameter increased, with smaller particles having volatile mass fraction of ∼20%. This result was further confirmed by chemical characterization of size-selected particles, proving the robustness of online aerosol measurements.

Type:	Article
Title:	A comparative study on effective density, shape factor, and volatile mixing of non-spherical particles using tandem aerodynamic diameter, mobility diameter, and mass measurements
Open access status:	An open access version is available from UCL Discovery
DOI:	10.1016/j.jaerosci.2021.105930
Publisher version:	https://doi.org/10.1016/j.jaerosci.2021.105930
Language:	English
Additional information:	This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords:	Tandem measurement, Effective density, Dynamic shape factor, Volatile mixing, Non-spherical, Soot
UCL classification:	UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI:	https://discovery.ucl.ac.uk/id/eprint/10140530