Atmospheric microplastic deposition in a valley city over a five-year period: sources, ecological risks, spatiotemporal distributions and influencing factors

In this study, the spatiotemporal distributions, influencing factors, sources, and ecological risks of atmospheric microplastic deposition in a valley city from 2019 to 2023 were investigated. On average, dry deposition accounted for 75.90% of the microplastic deposition. The deposition fluxes exhibited significant spatiotemporal differences. The deposition fluxes in summer and winter were the highest (814.36 p m d, on average) and lowest (178.65 p m d, on average), respectively. The average annual and seasonal deposition fluxes were strongly influenced by the precipitation intensity and frequency, the frequency of daily average wind speeds ≥ 2 m s, the boundary layer height, the air temperature and the ultraviolet radiation dose. In addition, the average annual deposition fluxes were strongly influenced by the inner city travel intensity and number of tourists, and the average seasonal deposition fluxes were strongly influenced by the seasonal precipitation amount. The spatial distributions of deposition fluxes were influenced by population density. Approximately 42.11% of the microplastic deposition originated from local sources, and the nonlocal sources were mainly from the northwestern region of the study area. The pollution level, hazard level and ecological risk of microplastic deposition during the pandemic period were lower than those during the non-pandemic period. Our results suggested that atmospheric microplastic deposition was influenced by both natural and anthropogenic factors.