The settling of microplastics (MPs) in the initial acceleration fall stage, i.e., before reaching the terminal settling velocity, has not been investigated, which is however important for understanding MP transport and fate. MP disks sized 3–5 mm, of three shapes and made of three polymers (1.038–1.343 g/cm) were examined. Five release ways and three release angles (0°, 45°, 90°) were used. MP disks with the release angle of 0° start to zigzag immediately after the release, while the MP disks with the release angles of 45° and 90° first adjust to a horizontal position and then zigzag. The adjustment distances in the vertical and horizontal directions, as well as the maximum vertical settling velocity, are influenced by MP density, size, release angle and release way. The detailed settling trajectory and velocity were also analyzed. Finally, the time-changing drag coefficient of MP disks was examined and discussed.

中文翻译：

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微塑料盘在加速跌落过程中的沉降行为

微塑料 (MP) 在初始加速下降阶段（即达到最终沉降速度之前）的沉降尚未得到研究，但这对于理解 MP 的运输和归宿非常重要。对尺寸为 3-5 毫米、具有三种形状并由三种聚合物 (1.038-1.343 g/cm) 制成的 MP 盘进行了检查。使用了五种释放方式和三种释放角度（0°、45°、90°）。释放角度为0°的MP盘在释放后立即开始锯齿状移动，而释放角度为45°和90°的MP盘则先调整到水平位置然后锯齿状移动。垂直和水平方向的调节距离以及最大垂直沉降速度受MP密度、尺寸、释放角度和释放方式的影响。还分析了详细的沉降轨迹和速度。最后，对 MP 盘随时间变化的阻力系数进行了检验和讨论。