Abstract. Volcanic ash is known to nucleate ice when immersed in supercooled water droplets. This process may impact the properties and dynamics of the eruption plume and cloud, as well as those of meteorological clouds once the ash is dispersed in the atmosphere. However, knowledge of what controls the ice-nucleating effectiveness (INE) of ash remains limited, although it has been suggested that crystalline components in ash may play an important role. Here we adopted a novel approach using nine pairs of tephra and their remelted and quenched glass equivalents to investigate the influence of chemical composition, crystallinity and mineralogy on ash INE in the immersion mode. For all nine pairs studied, the crystal-bearing tephra nucleated ice at higher temperatures than the corresponding crystal-free glass, demonstrating that crystalline phases are key to ash INE. Similar to findings for desert dust from arid and semi-arid regions, the presence of feldspar minerals characterises the four most ice-active tephra samples, although a high INE is observed even in the absence of alkali feldspar in samples bearing plagioclase feldspar and orthopyroxene. There is evidence of a potential indirect relationship between chemical composition and ash INE, whereby a magma of felsic to intermediate composition may generate ash containing ice-active feldspar minerals. This complex interplay between chemical composition, crystallinity, and mineralogy could help partly to explain the variability in volcanic ash INE reported in the literature. Overall, by categorically demonstrating the importance of crystalline phases in the INE of volcanic ash, our study contributes insights essential for better appraising the role of airborne ash in ice formation. Among these is the inference that glass-dominated ash emitted by the largest explosive eruptions may be less effective at impacting ice-nucleating particle populations than crystalline ash generated by smaller, more frequent eruptions.
Ice morphology modification and solute recovery improvement by heating and annealing during block freeze-concentration of coffee extracts