Influence of settling/rising velocity on the vertical distribution of microplastics in the marine environment

The problem of microplastic contamination in marine environment is addressed using a three-dimensional Lagrangian dispersion model. The dispersion model tracks the trajectories of virtual particles influenced by mean ocean currents derived from an oceanographic model and subgrid-scale turbu-1ence parameterized in the model itself. For the vertical component, the specific characteristics of microplastics are considered through their terminal settling/rising velocity. Dispersion models typically investigate the influence of terminal settling/rising velocity by performing simulations, where all particles are assigned the same velocity value. To conduct a simulation with virtual particles having diverse physical characteristics (sizes, shapes, and densities), a spectrum of settling/rising velocities was generated to model the wide variety of microplastics present in the sea. The results show that using a probability distribution for set-tling/rising velocity, considering the diverse spectrum of mi-croplastics present in the ocean, is essential and significantly alters both qualitatively and quantitatively the vertical concentration profiles throughout the water column.