Shielded collectors improve the capture of atmospheric microplastic deposition

Atmospheric microplastic deposition is widely measured using unshielded bulk precipitation or wet-only collectors; however, depending on their design, these collectors may be prone to significant undercatch due to wind-induced resuspension and aerodynamic turbulence. Here we show that shielded collectors captured significantly higher microplastic (mp) deposition (>3 times) than unshielded designs (p < 0.05, Kruskal-Wallis), with median daily microplastic deposition rates of 20-28 mp/m²/day compared to 6-11 mp/m²/day in unshielded collectors, underscoring the potential influence of wind on catch efficiency. Further, dry deposition dominated over wet, representing up to 60 ± 19% of bulk deposition in the shielded collector at one of our study sites. These results suggest that collector design may have a substantial effect on deposition estimates, which could have implications for estimates of microplastic budgets, retention in terrestrial and aquatic ecosystems, and our ability to constrain the atmospheric limb of the plastic cycle. These results not only highlight the need to harmonize atmospheric sampling methods but also the need to standardize the use of shielded collectors.