The Shape-Selective Suspension–Deposition Differentiation of Microplastics in an Air–Snow System: Insights from a Northeastern Polluted City in China

Atmospheric microplastics (MPs) are increasingly recognized as important atmospheric pollutants, yet the role of particle physical properties in their suspension-deposition differentiation remains unclear. Here, MPs were simultaneously investigated in 31 total-suspended-particulate samples and 16 surface snow samples during a one-month winter period dominated by dry deposition in Changchun, Northeast China. Atmospheric MPs average 20.28 ± 5.62 MPs·m-3 (3.70 ± 1.55 μg·m-3). Snow MPs exhibit a cumulative behavior over time, with a mean concentration of (4.45 ± 2.32) × 104 MPs·L-1 ((1.49 ± 1.03) × 104 μg·L-1) and an average deposition load of (5.06 ± 2.74) × 105 MPs·m-2 ((1.74 ± 1.25) × 105 μg·m-2). Temporal patterns show that the proportions of fibers and films increase in the atmosphere but decrease in snow, whereas foams show the opposite trend. Particle shape best explains the differentiation of MPs between air and snow: deposited MPs exhibit higher sphericity and lower aspect ratios (ARs), whereas suspended MPs show an inverse pattern. Enrichment index analysis further confirms that AR is significantly associated with snow enrichment. These results provide direct field evidence for shape-selective enrichment of atmospheric MPs in snowpack under dry deposition dominated winter conditions in an urban environment.