Plastic pollution is one of the most pressing environmental and social issues of the 21st century. Recent work has highlighted the atmosphere’s role in transporting microplastics to remote locations [S. Allen et al., Nat. Geosci. 12, 339 (2019) and J. Brahney, M. Hallerud, E. Heim, M. Hahnenberger, S. Sukumaran, Science 368, 1257–1260 (2020)]. Here, we use in situ observations of microplastic deposition combined with an atmospheric transport model and optimal estimation techniques to test hypotheses of the most likely sources of atmospheric plastic. Results suggest that atmospheric microplastics in the western United States are primarily derived from secondary re-emission sources including roads (84%), the ocean (11%), and agricultural soil dust (5%). Using our best estimate of plastic sources and modeled transport pathways, most continents were net importers of plastics from the marine environment, underscoring the cumulative role of legacy pollution in the atmospheric burden of plastic. This effort uses high-resolution spatial and temporal deposition data along with several hypothesized emission sources to constrain atmospheric plastic. Akin to global biogeochemical cycles, plastics now spiral around the globe with distinct atmospheric, oceanic, cryospheric, and terrestrial residence times. Though advancements have been made in the manufacture of biodegradable polymers, our data suggest that extant nonbiodegradable polymers will continue to cycle through the earth’s systems. Due to limited observations and understanding of the source processes, there remain large uncertainties in the transport, deposition, and source attribution of microplastics. Thus, we prioritize future research directions for understanding the plastic cycle.

塑料污染是 21 世纪最紧迫的环境和社会问题之一。最近的工作强调了大气在将微塑料运输到偏远地区方面的作用 [S. 艾伦等人，Nat。地球科学。12, 339 (2019) 和 J. Brahney、M. Hallerud、E. Heim、M. Hahnenberger、S. Sukumaran，科学368, 1257–1260 (2020)]。在这里，我们使用微塑料沉积的原位观测结合大气传输模型和最佳估计技术来测试最可能的大气塑料来源的假设。结果表明，美国西部的大气微塑料主要来自二次再排放源，包括道路 (84%)、海洋 (11%) 和农业土壤灰尘 (5%)。使用我们对塑料来源和模拟运输路径的最佳估计，大多数大陆是海洋环境塑料的净进口国，这强调了遗留污染在塑料大气负担中的累积作用。这项工作使用高分辨率的空间和时间沉积数据以及几个假设的排放源来限制大气塑料。类似于全球生物地球化学循环，塑料现在以不同的大气、海洋、冰冻圈和陆地停留时间在全球范围内盘旋。尽管可生物降解聚合物的制造取得了进展，但我们的数据表明，现存的不可生物降解聚合物将继续在地球系统中循环。由于对来源过程的观察和了解有限，微塑料的运输、沉积和来源归属仍然存在很大的不确定性。因此，我们优先考虑未来的研究方向，以了解塑料循环。我们的数据表明，现存的不可生物降解的聚合物将继续在地球系统中循环。由于对来源过程的观察和了解有限，微塑料的运输、沉积和来源归属仍然存在很大的不确定性。因此，我们优先考虑未来的研究方向，以了解塑料循环。我们的数据表明，现存的不可生物降解的聚合物将继续在地球系统中循环。由于对来源过程的观察和了解有限，微塑料的运输、沉积和来源归属仍然存在很大的不确定性。因此，我们优先考虑未来的研究方向，以了解塑料循环。