Shape matters: long-range transport of microplastic fibers in the atmosphere

TL;DR

This study demonstrates that the non-spherical shape of microplastic fibers significantly enhances their atmospheric transport, allowing them to reach remote regions and potentially impact the stratospheric ozone layer.

Contribution

The paper introduces laboratory measurements of microplastic fiber settling velocities and incorporates shape effects into atmospheric transport models, revealing increased long-range transport potential.

Findings

Fibers settle 76% slower than spheres of the same volume.

Microplastic fibers can reach remote regions like the High Arctic.

Fibers can ascend to the stratosphere, risking ozone layer damage.

Abstract

Deposition of giant microplastic particles from the atmosphere has been observed in the most remote places on Earth. However, their deposition patterns are difficult to reproduce using current atmospheric transport models. These models usually treat particles as perfect spheres, whereas the real shapes of microplastic particles are often far from spherical. Such particles experience lower settling velocities compared to volume-equivalent spheres, leading to longer atmospheric transport. Here, we present novel laboratory experiments on the gravitational settling of microplastic fibers in air and find that their settling velocities are reduced by up to 76% compared to spheres of the same volume. An atmospheric transport model constrained with the experimental data shows that shape-corrected settling velocities significantly increase the horizontal and vertical transport of particles. Our model results show that microplastic fibers of about 1 mm length emitted in populated areas can reach extremely remote regions of the globe, including the High Arctic, which is not the case for spheres. We also calculate that fibers with lengths of up to 100 {\mu}m settle slowly enough to be lifted high into the stratosphere, where degradation by ultraviolet radiation may release chlorine and bromine, thus potentially damaging the stratospheric ozone layer. These findings suggest that the growing environmental burden and still increasing emissions of plastics pose multiple threats to life on Earth.