The ice nucleation properties and its parameterization for fly ash particles
Shushan Cong^1,2, Bingbing Wang^1,2
1College of Ocean and Earth Sciences, Xiamen University, China
²State Key Laboratory of Marine Environmental Science (Xiamen University)
*Bingbing.Wang@xmu.edu.cn
Abstract: Combustion processes are significant sources of atmospheric particulate matter. These combustion-derived particles can act as cloud condensation nuclei and potentially as ice-nucleating particles, thereby affecting cloud properties and Earth’s climate. Here, we investigate how the physicochemical properties of fly ash (FA) from different combustion plants control immersion freezing ability. We found that fly ash from different sources showed distinct ice-nucleating activities, with median freezing temperatures (T₅₀) at 0.1 wt% ranging from 250.7 to 259.4 K and above water blank (247.9 K). The effect of chemical aging by ammonium sulfate and sulfuric acid on Ice nucleation of FA was investigated. Ammonium sulfate (0.05 M) aging generally enhanced T₅₀ for LY-FA, SRM2689, and SRM2690 (+0.2 to +1.4, +1.6 to +3.6, and +0.4 to +2.2 K, respectively), whereas XM-FA and SRM2691 increased at lower concentrations but decreased at 0.1 wt% (−2.9 K) and 0.85 wt% (−1.1 K), respectively. At 0.1 wt%, sulfuric acid aging increased T₅₀ for LY-FA (+1.3 K) and SRM2689 (+0.6 K), but decreased for XM-FA (−0.5 K), SRM2690 (−1.4 K), and SRM2691 (−0.9 K). Our results suggest that the immersion freezing activity of FA is mainly controlled by calcium- and sulfur-containing components, and is further modified by chemical aging through a balance between surface activation and suppression effects. We provide the corresponding parameterization schemes for immersion freezing by FA. This study improves our understanding of the role of FA in ice crystal formation and supports better assessment of their impacts on climate and precipitation.

Keywords：fly ash, INPs, single particle analysis, immersion freezing