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A Model for Dry Deposition of Atmospheric Micro- and Nanoplastic Fibers
Summary
Scientists built a computer model to predict how tiny plastic fibers floating in the air eventually settle back down to Earth, something we didn't fully understand before. The surprising finding: the smallest fibers, right at the border between "micro" and "nano" size, can stay airborne for over four months, meaning they can travel huge distances and stay in the air we breathe far longer than expected. This matters because it means these tiny plastic particles may be more widespread in our atmosphere than previously thought, raising questions about how much we're inhaling and where this pollution ends up.
Atmospheric microplastics and nanoplastics (MNPs), particularly fibers, are emerging contaminants with complex deposition dynamics that remain poorly understood. Here, a mechanistic dry deposition model is developed for MNP fibers, integrating gravitational settling, Brownian diffusion, impaction, and interception. The model incorporates fiber-specific drag corrections and shape-dependent diffusivity to estimate total deposition velocity across a range of particle lengths and aspect ratios. Results show that total deposition velocity deviates significantly from gravitational settling alone, especially for submicron fibers. Global simulations reveal strong spatial and seasonal variability driven by land cover and turbulence. Atmospheric lifetime estimates based on dry deposition indicate that micro - nano transition fibers (∼ 1 μm) persist longest in the boundary layer, with dry-deposition lifetimes exceeding four months (∼ 2,900 h). This framework supports the integration of MNP fibers into existing aerosol dry-deposition schemes in regional and global atmospheric models and improves predictions of their environmental fate.