Fahy William D, Maters Elena C, Giese Miranda Rona, Adams Michael P, Jahn Leif G, Sullivan Ryan C, Murray Benjamin J
Center for Atmospheric Particle Studies, Carnegie Mellon University Pittsburgh, Pennsylvania 15213 USA.
School of Earth and Environment, University of Leeds Leeds LS2 9JT UK.
Environ Sci Atmos. 2021 Dec 22;2(1):85-99. doi: 10.1039/d1ea00071c. eCollection 2022 Jan 20.
Volcanic ash nucleates ice when immersed in supercooled water droplets, giving it the potential to influence weather and climate from local to global scales. This ice nucleation activity (INA) is likely derived from a subset of the crystalline mineral phases in the ash. The INA of other mineral-based dusts can change when exposed to various gaseous and aqueous chemical species, many of which also interact with volcanic ash in the eruption plume and atmosphere. However, the effects of aqueous chemical aging on the INA of volcanic ash have not been explored. We show that the INA of two mineralogically distinct ash samples from Fuego and Astroni volcanoes is variably reduced following immersion in water or aqueous sulfuric acid for minutes to days. Aging in water decreases the INA of both ash samples by up to two orders of magnitude, possibly due to a reduction in surface crystallinity and cation availability accompanying leaching. Aging in sulfuric acid leads to minimal loss of INA for Fuego ash, which is proposed to reflect a quasi-equilibrium between leaching that removes ice-active sites and dissolution that reveals or creates new sites on the pyroxene phases present. Conversely, exposure to sulfuric acid reduces the INA of Astroni ash by one to two orders of magnitude, potentially through selective dissolution of ice-active sites associated with surface microtextures on some K-feldspar phases. Analysis of dissolved element concentrations in the aged ash leachates shows supersaturation of certain mineral species which could have precipitated and altered the INA of the ash. These results highlight the key role that leaching, dissolution, and precipitation likely play in the aqueous aging of volcanic ash with respect to its INA. Finally, we discuss the implications for understanding the nature and reactivity of ice-active sites on volcanic ash and its role in influencing cloud properties in the atmosphere.
火山灰浸入过冷水滴中时会使水结冰，这使其有可能在从局部到全球的尺度上影响天气和气候。这种冰核活性（INA）可能源自火山灰中结晶矿物相的一个子集。其他矿物基粉尘的INA在暴露于各种气态和水性化学物质时会发生变化，其中许多化学物质也会在火山喷发羽流和大气中与火山灰相互作用。然而，水性化学老化对火山灰INA的影响尚未得到研究。我们表明，来自富埃戈火山和阿斯特罗尼火山的两种矿物成分不同的火山灰样本，在浸入水或硫酸水溶液中数分钟至数天后，其INA会有不同程度的降低。在水中老化会使两种火山灰样本的INA降低多达两个数量级，这可能是由于浸出过程中表面结晶度降低和阳离子可用性减少所致。在硫酸中老化导致富埃戈火山灰的INA损失最小，这被认为反映了去除冰活性位点的浸出与辉石相上揭示或产生新位点的溶解之间的准平衡。相反，暴露于硫酸会使阿斯特罗尼火山灰的INA降低一到两个数量级，这可能是通过选择性溶解与某些钾长石相表面微观纹理相关的冰活性位点实现的。对老化火山灰浸出液中溶解元素浓度的分析表明，某些矿物物种过饱和，可能已经沉淀并改变了火山灰的INA。这些结果突出了浸出、溶解和沉淀在火山灰水性老化过程中对其INA可能发挥的关键作用。最后，我们讨论了这些结果对于理解火山灰上冰活性位点的性质和反应性及其在影响大气中云特性方面作用的意义。
