Reconciling modeled and observed atmospheric microplastics: a physically consistent framework reduces global emission estimates by a factor of 2

Atmospheric transport is central to the global cycling of microplastics, yet model-based estimates of emissions, concentration, and deposition remain highly uncertain. A critical challenge arises from the mismatch between models, which simulate microplastics as mass-based tracers, and observations, which are typically reported as particle counts and are often limited by microscopy techniques that fail to detect the smallest modeled particles.To address this, we extend previous work1 and use the GEOS-Chem global chemical transport model to simulate atmospheric microplastic emissions, transport, and removal. We develop a physically consistent framework to reconcile simulations with observations by: (i) deriving a size distribution for atmospheric microplastics from literature data; (ii) extrapolating observations to the model’s size range, and (iii) converting particle counts to mass using literature-based assumptions about shape and density.Our results show that this framework reduces simulated global emissions by a factor of 20, with the contribution of marine sources decreasing from over 50% to just 20% of total emissions. The revised global emission estimate (~15 Gg/year) aligns with recent studies suggesting lower emissions than previously thought.2,3 Our findings highlight the need for standardized experimental methods, reporting of particle size distributions, and consistent frameworks to compare modeled and observed microplastics.References:1. Fu, Y. et al. Modeling atmospheric microplastic cycle by GEOS-Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions. One Earth 6, 705–714 (2023). 2. Bucci, S., Richon, C. & Bakels, L. Exploring the Transport Path of Oceanic Microplastics in the Atmosphere. Environ. Sci. Technol. 58, 14338–14347 (2024).3. Yang, S., Brasseur, G., Walters, S., Lichtig, P. & Li, C. W. Y. Global atmospheric distribution of microplastics with evidence of low oceanic emissions. Npj Clim. Atmospheric Sci. 8, 1–10 (2025).