Immersion Freezing Properties of Salt-Affected Soil and Salt Crust Particles from Northwestern China
Yingjie Zhou^1,2, Jun Li^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: Heterogeneous ice nucleation by atmospheric aerosols plays a critical role in cloud formation and evolution, thereby regulating precipitation, radiative budgets, and climate variability. In this study, samples of Salt-Affected Soils (SAS) and Salt Crusts (SCS) were collected from Inner Mongolia and the Qaidam Basin in northwestern China to investigate their heterogeneous ice nucleation behavior. The ice nucleating activity of these particles was examined across a range of mass concentrations with loess samples from the Loess Plateau included for comparison. The loess samples exhibited the highest ice nucleating efficiency. The median freezing temperature (T₅₀) decreased from 265.4 ± 1.1 K at 1.0 × 10^-2 wt% to 251.4 ± 1.2 K at 1.0 × 10^-5 wt%. At 1.0 × 10^-5 wt%, the six SCS samples exhibited weak ice nucleation activity, with a mean T₅₀ of 246.3 K (245.1–247.1 K), whereas the four SAS samples exhibited higher ice nucleation activity than the SCS samples but lower activity than the loess samples, with a mean T₅₀ of 248.8 K (247.3–250.6 K). Notably, the SCS samples exhibited pronounced freezing plateaus in their frozen fraction curves at concentrations of 1.0 × 10^-3 and 1.0 × 10^-4 wt%, followed by a rapid increase in freezing probability, indicative of a two-stage freezing behavior. This observation suggests the presence of two distinct populations of heterogeneous ice active components. Overall, our findings demonstrate that SAS and SCS from northwestern China possess markedly different heterogeneous ice nucleation properties. These results provide new insights into the role of SAS and SCS particles in aerosol-cloud interactions and for improving the parameterization of their ice nucleating activity in atmospheric models.

Keywords: Ice nucleating particles, Salt-Affected Soils, Salt Crusts, Immersion freezing