Unveiling the Hidden Load: High Flux and Deposition Dynamics of Atmospheric Microplastics in the North China Plain

Atmospheric microplastics (MPs) play an important role in the transport of MPs across diverse environmental media, yet their annual deposition dynamics across heterogeneous urban–cropland regions remain poorly understood. We conducted a one-year field campaign at three contrasting sites in the North China Plain (NCP): Beijing (BJ, urban), Tianjin (TJ, industrial/coastal), and Handan (HD, agricultural). Atmospheric bulk-deposition samples were characterized for particle deposition rates, size, morphology, and polymer composition, with observations evaluated using meteorological and land-cover information. Deposition rates were significantly higher in BJ than in TJ (p < 0.05) and HD (p < 0.001). Median (interquartile range) deposition rates were 34640 (18703–90472), 14367 (6000–25810), and 6990 (3903–11790) items m–2 d–1 in BJ, TJ, and HD, respectively. Small particles (20–50 μm) dominated particle abundance (80.7%), whereas fragments dominated particle morphology (90.4%). Backward trajectories indicated seasonal differences in potential air-mass transport pathways. Integrating particle mass estimates with land-cover data yielded order-of-magnitude estimates of annual atmospheric MP inputs of approximately 6 Gg to urban areas and 17 Gg to cropland in the northern NCP. These results reveal pronounced spatiotemporal variability in atmospheric MP deposition and highlight the dominance of small MP fragments across urban and cropland ecosystems.