The dynamics and aggregation of microplastics in marine environments are investigated through high-fidelity direct numerical simulations with Lagrangian point-particle tracking. The properties of microplastics and biogenic particles, including size, density, and concentration, align with scenarios typical of seawater systems. The stickiness nature of microplastics, induced by biofilm formation (biofouling), is modeled through coagulation efficiency (stickiness parameter), which represents the probability of aggregation following a collision event. Two main aspects are at the core of the present work: analyzing the mechanisms of collision and coalescence between microplastics and biogenic particles, along with their spatial distribution, and characterizing the emerging aggregates. The results indicate that particles stickiness, concentration and (especially) size impact on the collision and coalescence rates. Furthermore, microplastics exhibit a strong tendency to accumulate near biogenic particles, leading to the creation of hetero-aggregates whose tendency to sink supports the general hypothesis of “missing microplastics”. Particularly, in cases where microplastics and biogenic particles are evenly concentrated, microplastics primarily contribute to the formation of aggregates. The stickiness mainly determines the most complex and large aggregates, which are less than 1% of the total.

中文翻译：

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凝结特性对上层海洋湍流中微塑料聚集的影响


通过拉格朗日点粒子跟踪的高保真直接数值模拟研究海洋环境中微塑料的动力学和聚集。微塑料和生物颗粒的特性，包括大小、密度和浓度，与海水系统的典型情况一致。由生物膜形成（生物污垢）诱导的微塑料的粘性性质是通过凝结效率（粘性参数）建模的，该参数表示碰撞事件后聚集的概率。目前工作的核心有两个主要方面：分析微塑料和生物颗粒之间的碰撞和聚结机制，以及它们的空间分布，并表征新出现的聚集体。结果表明，颗粒的粘性、浓度和（特别是）大小都会影响碰撞和聚结速率。此外，微塑料表现出在生物颗粒附近积累的强烈趋势，导致产生异质聚集体，其下沉趋势支持“缺失微塑料”的一般假设。特别是，在微塑料和生物颗粒均匀浓缩的情况下，微塑料主要有助于形成聚集体。粘性主要决定最复杂、最大的聚集体，占总量的 1% 以下。