Tire Wear Particles Outnumber Other Atmospheric Micro- and Nanoplastics across Rural to Suburban School Sites

Knowing the identities, origins, and magnitude of plastic pollution in the atmosphere is critical to understanding their impacts on human health and ecosystems. In particular, atmospheric micro- and nanoplastics (MNPs) in outdoor locations with unique atmospheric sources, such as freshwater in the Midwest United States, require additional research. In this work, we used active and passive air sampling techniques to characterize atmospheric MNPs across ten months in school parking lots of three Michigan counties. Particles were manually identified using optical-photothermal infrared plus Raman spectroscopy combined with database-matching predictions with 90% statistical confidence. For some particles, additional morphological and elemental information was obtained using scanning electron microscopy with energy dispersive X-ray spectroscopy. Across all sampling techniques, locations, and seasons, we found that mean and median number concentrations of atmospheric plastics was 1% of all particles, with tire wear particles outnumbering nontire MNPs by a factor of 3. Importantly, we illustrate that nanoplastics make up greater than 60% of MNPs by aerodynamic diameter, drawing attention to an understudied size class in the environment. Insights from this work will aid efforts to understand spatiotemporal influences on atmospheric plastic concentration, transport, and fate in the environment.