Is plastic dust different from mineral dust? Results from idealized wind tunnel experiments.

Atmospheric transport has been shown to effectively disperse microplasticparticulate matter to virtually every environment on the planet. Despite thisefficient long-range transport, only few studies have examined the fundamentalmechanisms of the atmospheric transport of microplastics. Here, we present theresults of wind tunnel experiments, examining the detachment behavior of plasticparticles ranging from 38 to 125 µm in diameter from flat substrates.Detachment was achieved solely by aerodynamic forces of the turbulent airflow.The detachment behavior of spheric microplastic particles (Polyethylene) andspheric glass microparticles (Borosilicate) of nominally the same diameter(63-75 µm) are contrasted across substrates with hydrophilic to hydrophobicsurface coatings. We further examine the effect of particle-particle collisions onthe detachment behavior of both Polyethylene and glass spheres. The criticalfriction velocity (u*,th), which is defined as the value at which 50% of allmicroparticles detach, ranged from 0.1 to 0.3 ms −1. Particle-particle collisionsreduced the u*,th of glass, but not that for PE. Results were compared withpredictions of a Jonhson-Kendall-Roberts model. The relation of diameter tou*,th compared well between results and prediction for Polyethylene spheres.Glass spheres were predicted to detach at smaller u*,th than polyethylenespheres, but detached at higher u*,th. Here, we argue that capillary forcesincreased the adhesion, which is not covered by the model. The combination ofparticle and substrate hydrophobicity influenced the relative humidity, at whichcapillary forces increased u*,th.