Physical–chemical properties of particles in hailstones from central Argentina

Abstract. This study presents a novel analysis of two hailstones collected in central Argentina to provide insights into the size distribution, composition, and potential sources of non-soluble particles within hailstones. Using this new method, non-soluble particles are trapped beneath a thin layer of polyvinyl resin and analyzed with confocal laser and scanning electron microscopy combined with energy-dispersive spectroscopy, preserving their in situ location and physical characteristics. The study characterized these particles' distribution, shape, and size and identified their elemental composition, which is used to interpret possible source regions. Particles ranged in diameter from our detection limit from 1 to 256 µm, with the largest particles consistently found in the hailstone embryos. Agglomerated mineral and organic particles dominated the elemental composition in both the embryo and outer layers, with the largest agglomerated particle (256 µm) being an organic-rich particle in the embryo of the larger hailstone. The composition and size distribution varied between the two hailstones: one contained agglomerated salt particles (up to 150 µm) in its embryo, traced to a nearby salt lake, while the other contained copper chloride and zinc chloride particles (up to 78 µm) primarily in its outer layers, potentially associated with agrochemicals commonly used for pest control and fertilizer in Argentina. Various local and regional land-use types, including shrublands, mixed vegetation, croplands, and urban areas, were linked to specific types of particles. Therefore, this study highlights the regional influence of various land-use types on hail formation and growth, pointing to the potential impacts of natural and anthropogenic factors on hailstone composition and revealing how particle characteristics vary between the embryo and outer layers of hailstones.