High Optical and Temporal Resolution Investigations into Non-Ideal Resuspension Phenomena

EDWARD NEAL, Lukesh K. Mahato, Richard J. Thomas, Maurice Walker, Jack Vincent, Simon Parker, Virginia Foot, Emily Kruger, Jonathan P. Reid, University of Bristol

     Abstract Number: 176
     Working Group: Aerosol Physics

Abstract
Particle resuspension is omnipresent in our lives with activities such as cleaning, walking and driving all contributing to resuspended aerosol concentrations. However, this phenomenon is rarely captured in aerosol dispersion simulations as existing resuspension models are constrained by a lack of understanding on the influence of complex governing factors. Particle morphology is one such influence and forms the focus of this study that incorporates a novel approach for fabricating and resuspending particles of reproducible irregular shapes.

Our method, that was previously validated in work by Neal et al. (Aerosol Sci. and Tech., 58(12), 1389–1404, 2024), partners a quadrupole electrodynamic trap (the QuadFab) with a 3D printed wind tunnel. Within the QuadFab, aerosol droplets are suspended and dried under controlled relative humidity (RH) conditions. Varying this RH adapts the morphology of the resulting particles that are then deposited and resuspended in the wind tunnel. Particle detachment is monitored by a camera positioned below the apparatus that acquires images at 100 frames per second (FPS).

The resuspension efficiencies of two morphologies of NaCl particles, framboidal and platelet-like in shape, will be presented. The framboidal particles demonstrated a greater susceptibility for resuspension than the platelets. However, the mechanistic reasons for this difference in resuspension behavior remained elusive with wind tunnel studies alone. To further study these variations in particle detachment, individual resuspension events featuring the two particle morphologies were captured at 64000 FPS with a high frame rate camera. This technique allows for greater optical and temporal resolution analysis of particle orientation, particle-surface contact and particle rotation during resuspension. The latter component provides insight into the contributions of the aerodynamic forces, lift and drag, during resuspension events. Initial observations with the NaCl particles indicated that lift likely provides a greater contribution to their detachment than would be assumed for spherical particles.