Integrated assessment of fibrous vs. non-fibrous microplastic deposition patterns in subtropical urban atmospheres: From morphotypes to risk vectors

Airborne microplastics (AMPs) have drawn increasing scientific attention in recent years owing to their long-range transport potential and demonstrated risks to the environment and human health. This investigation systematically examines AMP characteristics in Macao, focusing on their: (1) spatiotemporal distribution patterns, (2) morphological and chemical profiles, (3) key influencing factors, and (4) associated ecological risks. Notably, a shape-stratified analysis was implemented, differentiating fibrous from non-fibrous AMP fractions, followed by comparative analysis against unfiltered shape aggregates. Substantial spatial variability in AMP deposition fluxes across Macao was revealed, with values ranging from 114 ± 77 to 1164 ± 651 MP/m/day (mean: 517 ± 457 MP/m/day). Population density emerged as the strongest predictor of spatial AMP variability (p < 0.01), exhibiting exponential relationships with deposition fluxes. Meteorological parameters displayed distinct shape-dependent influence patterns across monitoring locations. A positive correlation emerged between AMP abundances and inhalable particulate matter (PM) concentrations (r > 0.71, p < 0.05), suggesting potential co-production and co-transport mechanisms. Maximum wind velocity was identified as critical drivers of short-term AMP flux variations, potentially through aerosolization of terrestrial plastic reservoirs. The backward trajectory results emphasized the influence of wind and air mass sources. Finally, the potential ecological risk was used as an example to illustrate the limitations of existing risk assessment models for AMP. This work establishes microplastic morphology as a critical mediator in atmospheric transport dynamics, quantitatively demonstrates the dual anthropogenic-meteorological control of AMP distributions, and provides new insights into the factors affecting the spatiotemporal variation of the abundance.