Geometric Form and Density Govern Microplastic Particle Kinetics During Aeolian Transport

Microplastics (MP) have been found in most terrestrial areas of the Earth including rural, remote and isolated locations where the only expected source is through atmospheric transport and deposition. Currently, there has been limited research on the mechanics of microplastic transport by wind, and in particular, the similarities and differences between the motion of mineral grains and microplastic particles within boundary layer flows. Such information is needed to lay the foundation for the development of models of mineral-microplastic interaction during transport in the environment. This study examines the influence of geometric form on the dynamics of microplastic particle entrainment and transport by wind. Using high speed photography, a series of particle tracking velocimetry (PTV) measurements were obtained in wind tunnel experiments to quantify and compare the kinetics of nylon fibres (volume equivalent spherical diameter (d_eq) of 314 µm ),  polyethylene terephthalate fragments (d_eq=215 µm), polyethylene spheres (d_eq=182 µm), and quartz sand (d_eq=267 µm) during flight within a wall bounded airflow. Particular attention is given to quantifying the 2D velocity components of each particle as it approached and impacted the bed surface, as compared to the consequent rebound/ejection event. Preliminary results show that microplastic particles—particularly spheres, fragments, and fibres—exhibit higher transport velocities than quartz sand but impact the surface at shallower angles. These findings suggest that existing sediment transport models may require adaptation to account for the distinct behaviours of microplastics in aeolian systems.