Modeling of vertical microplastic transport by rising bubbles

Abstract

AbstractMicroplastic particle concentration at the sea surface is critical for quantifying microplastic transport across the water-air interface. Previous studies suggest that the concentration at the sea surface is enhanced compared to bulk concentration, yet little is known about the detailed mechanisms behind this enhancement. In this work, we model one particular process in simulation that may contribute to this enhanced surface concentration: bubble scavenging. Using lattice-Boltzmann Volume-of-Fluid simulations, we find that rising bubbles indeed generate a net flow of particles toward the surface. The efficiency of the process, however, highly depends on the microplastic particle surface properties. Clean, hydrophobic particles adhere much better to the bubble surface and are therefore transported significantly better than weathered, hydrophilic particles that are only entrained in the flow around a bubble.