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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.
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Constraining the atmospheric limb of the plastic cycle
Microplastic particles and fibers generated from the breakdown of mismanaged waste are now so prevalent that they cycle through the earth in a manner akin to global biogeochemical cycles. In modeling the atmospheric limb of the plastic cycle, we show that most atmospheric plastics are derived from the legacy production of plastics from waste that has continued to build up in the environment. Roads dominated the sources of microplastics to the western United States, followed by marine, agriculture, and dust emissions generated downwind of population centers. At the current rate of increase of plastic production (∼4% per year), understanding the sources and consequences of microplastics in the atmosphere should be a priority.
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- PAR ID:
- 10250944
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences of the United States of America
- Volume:
- 118
- Issue:
- 16
- ISSN:
- 1091-6490
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/https://doi.org/10.1073/pnas.2020719118
