The fine ash released into the atmosphere (particles <63 μm) during explosive volcanic eruptions represents a significant threat for both the ecosystem and many sectors of society. In order to mitigate the associated impact, ash dispersal models need to accurately estimate ash concentration through time and space. Since most fine ash sediments in the form of aggregates, ash dispersal models require a quantitative description of ash aggregation. The physical and chemical processes involved in the collision and sticking of volcanic ash have been extensively studied in the last few decades. Among the different factors affecting volcanic particle aggregation (e.g., turbulence, particle-particle adhesion, presence of liquid and solid water), the charge carried by volcanic particles has been found to play a crucial role. However, Coulomb interactions are not yet taken into account in existing models. In order to fill this gap, we propose a strategy to take charge into account. In particular, we introduce a quantitative model for aggregation of oppositely charged micron—to millimetre-sized objects settling in still air. Our results show that the presence of charge considerably enhances the collision efficiency when one of the colliding objects is very small (<20 µm), and that the sticking efficiency is not affected by particle charge if colliding objects are either small enough (<20 µm) or large enough (>200 µm). Besides providing a theoretical framework to quantify the effect of charge, our findings demonstrate that aggregation models that do not account for electrification significantly underestimate the amount of fine ash that sediments in the form of aggregates, leading to an overestimation of the residence time of fine ash in the atmosphere after explosive volcanic eruptions.

爆炸性火山喷发过程中释放到大气中的细灰（颗粒<63μm）对生态系统和社会许多部门均构成重大威胁。为了减轻相关的影响，灰分扩散模型需要通过时间和空间准确估算灰分浓度。由于大多数细粉尘以聚集体形式沉积，因此粉尘扩散模型需要对粉尘聚集进行定量描述。在过去的几十年中，对火山灰的碰撞和粘附所涉及的物理和化学过程进行了广泛的研究。在影响火山颗粒聚集的不同因素中（例如，湍流，颗粒与颗粒的粘附，液体和固体水的存在），已发现火山颗粒携带的电荷起着至关重要的作用。然而，现有模型中尚未考虑库仑相互作用。为了填补这一空白，我们提出了一项考虑充电的策略。特别是，我们引入了一个定量模型，用于将带相反电荷的微米聚集到沉降在静止空气中的毫米大小的物体上。我们的结果表明，当一个碰撞物体很小（<20 µm）时，电荷的存在会大大提高碰撞效率，并且如果碰撞物体足够小（<20 µm），则粘附效率不受粒子电荷的影响。 ）或足够大（> 200 µm）。除了提供量化电荷影响的理论框架外，