Event-Scale Deposition of Atmospheric Microplastics in Snowfall of the Sierra Nevada in North America

Abstract Atmospheric deposition of microplastics (MPs) at an event-scale resolution can be measured in snowfall events, as snow scavenges atmospheric MPs and the snowpack serves as a repository for MP accumulation. We monitored MP deposition in freshly fallen snow, the snowpack, and dry deposition over the course of 6 months in the Sierra Nevada of North America. Average microplastic concentrations in fresh snow ranged from 11.8 to 37.5 p/L at remote sites, which were significantly less than the 68.3 to 92.9 p/L MP concentrations found at the anthropogenically impacted site. Average bulk deposition rates were estimated to be 267 to 3190 p/m2/day at remote sites, significantly lower than the 3242 to 7480 p/m2/day at the anthropogenically impacted site. HYSPLIT back-trajectory modeling characterized the potential regional transport of MPs from upwind regions that were predominantly agricultural and suburban areas, as well as localized anthropogenic activities that could significantly affect MP deposition rates in snowfall. This study introduces high-throughput FTIR analysis methods with a highlight on fiber spectroscopy, demonstrates the value of estimating MP fluxes at the meteorological event scale, reports MP deposition rates in a critical water resource, and provides a basis for future long-term atmospheric MP monitoring.