Catching the variety: Obtaining the distribution of terminal velocities of microplastics particles in a stagnant fluid by a stochastic simulation

Abstract

A simple stochastic numerical model is applied to obtain the distribution of the terminal settling/rising velocity of a set of MPs particles whose size, shape, and density have their distributions in accordance with field observations and production trends. Results of the direct Monte Carlo simulation are shown to reproduce well the data of laboratory experiments. Distributions of MPs by size and density appear to be more valuable for the final terminal velocity distribution compared to the influence of the distribution by shape. The most “real” of the simulated distributions of the terminal velocity of MPs particles in the ocean has a multimodal shape, slightly different for fresh and saline waters. Multimodality arises from the fact that the terminal velocity depends on several physical parameters simultaneously and thus should be an expected feature of MPs terminal velocity distribution.