A Review of Atmospheric Micro/Nanoplastics: Insights into Source and Fate for Modelling Studies

Micro/nanoplastics (MNPs), as emerging pollutants, have attracted increasing attention due to their potential adverse effects on human health, ecosystems, and climate. The rapid, turbulent, and large-scale nature of atmospheric transport facilitates both horizontal and vertical movement of MNPs over long distances within a short time, largely independent of topographical constraints, thereby accelerating their global cycle and exacerbating their impacts. Research on the atmospheric life cycle of MNPs primarily relies on a combination of observations and numerical modelling, yet emission estimates remain the major source of uncertainty, posing substantial challenges for lifecycle assessment. This review synthesises findings from atmospheric observations and numerical modelling studies conducted over the past five years to examine the sources and long-range transport dynamics of MNPs, as well as the key factors influencing their transport, while also quantifying uncertainties in emission flux estimates. Two major uncertainties persist: the wide variability in marine emission estimates, which span four orders of magnitude, and the unresolved question of whether terrestrial or marine sources are the dominant contributors to atmospheric micro/nanoplastic emissions. Furthermore, this review highlights critical factors driving these uncertainties, including limited data availability, inconsistencies in observational methodologies, oversimplified simulations, and gaps in understanding atmospheric cycling mechanisms. Additionally, variations in the particle size ranges targeted by different observational and modelling studies hinder cross-comparisons and model evaluations, representing another important source of uncertainty. To address these issues, we call for establishing a global network of standardised observations, improving sampling and simulation practices, and incorporating artificial intelligence. These strategies will enhance our understanding of the complete atmospheric cycle of MNPs, paving the way for more effective environmental management and better-informed policy decisions.