High optical and temporal resolution investigations into the morphological factors that influence particle resuspension

Abstract

Particle resuspension is a multi-faceted phenomenon that can enhance the time a particle is airborne once dispersed into the environment. The complexity of particle resuspension poses a challenge for mechanistic models that currently struggle to disentangle the contributions of many influential factors to the resuspension process. Such variables include particle morphology, surface roughness and environmental conditions. In this study we isolate particle morphology and experimentally observe the difference in resuspension behavior between two morphologies of NaCl particles, fabricated using the QuadFab, a novel device for the controlled manufacture of aerosol particles for resuspension studies. Investigations with a small-scale 3D printed wind tunnel apparatus demonstrate a quantitative difference between the resuspension efficiency of framboidal and platelet-like NaCl particles of a similar size, with the former displaying a greater susceptibility for resuspension. It was not possible to evaluate the mechanism for this difference in resuspension behavior with wind tunnel measurements alone, so additional high frame rate imaging experiments of particle detachment events were performed to observe incipient particle motion at a high optical and temporal resolution. This is the first study to capture the resuspension of non-spherical particles at a sufficiently high frame rate to monitor rotational motion of particles in the immediate moments after detachment. Consequently, these high frame rate measurements provide insight into the influences of both the lift and drag aerodynamic forces in these non-idealized resuspension scenarios. Possible routes for introducing non-spherical particles into resuspension models are discussed with an assessment of the most relevant shape parameters.