Modeling atmospheric microplastic cycle by GEOS- Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions

The atmosphere plays a vital role in microplastic (MP) transport, facilitating continuous exchanges with land and ocean. However, the sources of atmospheric MP remain unclear. Previous studies suggested that the ocean is the primary source, with global emissions reaching up to 8,600 Gg year(-1). Here, we use global atmospheric abundance data, a newly developed atmospheric model, and optimal estimation to constrain the atmospheric sources. We find that the global atmospheric MP emissions are 324 (73-1,450) Gg year( -1). The ocean source is estimated to have a much smaller global emission (171 [38-764] Gg year( -1)] than previously believed, followed by road-related sources (115 [26-513] Gg year (-1)) including the suspension of tire and brake wears and mismanaged plastic waste. We simulate a net land-to-ocean transport by the atmosphere (25 Gg year (-1)). This highlights the importance of controlling terrestrial sources, and more data are needed to improve our understanding of the atmospheric MP cycle.