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Long-distance atmospheric transport of microplastic fibres influenced by their shapes
Summary
A new settling velocity model accounting for the actual flat shapes of microplastic fibers found that flat fibers have atmospheric residence times more than 450% longer than cylindrical equivalents, enabling far greater long-distance transport than previously estimated. This means microplastic fiber pollution is dispersed globally through the atmosphere far more efficiently than models assumed, reaching remote ecosystems and contributing to human inhalation exposure everywhere on Earth.
Recent studies have highlighted the importance of the atmosphere in the long-range transport of microplastic fibres. However, their dry deposition in the atmosphere is not fully understood, with the common spherical-shape assumption leading to significant uncertainties in predicting their travel distance and atmospheric residence time. Shapes of microplastic fibres vary greatly, which can be as long as 100 μm and as thin as 2 μm. Shapes of microplastic fibres may greatly affect their dry deposition in the atmosphere. Here we develop a theory-based settling velocity model for simulating atmospheric transport of microplastic fibres in different sizes and shapes. The model predicts a smaller aerodynamic size of microplastic fibres than that estimated by using volumetrically equivalent spherical counterparts. We find that the treatment of flat fibres as cylindrical ones, due to uncertainty in dimensions of sampled microplastic fibres, would cause overestimation of their dry deposition rate. Accounting for fibre thickness in sampled microplastic fibres leads to a mean enhancement of residence time by more than 450% compared to cylindrical ones. The results suggest a much more efficient long-range transport of flat fibres than previously thought. Flat microplastic fibres have much longer residence times and travel further in the atmosphere than previously appreciated, according to simulations of the settling of microplastics with different shapes.