Zobrist B, Marcolli C, Peter T, Koop T
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland.
J Phys Chem A. 2008 May 1;112(17):3965-75. doi: 10.1021/jp7112208. Epub 2008 Mar 26.
Heterogeneous ice nucleation experiments have been performed with four different ice nuclei (IN), namely nonadecanol, silica, silver iodide and Arizona test dust. All IN are either immersed in the droplets or located at the droplets surface. The IN were exposed to various aqueous solutions, which consist of (NH4)2SO4, H2SO4, MgCl2, NaCl, LiCl, Ca(NO3)2, K2CO3, CH3COONa, ethylene glycol, glycerol, malonic acid, PEG300 or a NaCl/malonic acid mixture. Freezing was studied using a differential scanning calorimeter and a cold finger cell. The results show that the heterogeneous ice freezing temperatures decrease with increasing solute concentration; however, the magnitude of this effect is solute dependent. In contrast, when the results are analyzed in terms of the solution water activity a very consistent behavior emerges: heterogeneous ice nucleation temperatures for all four IN converge each onto a single line, irrespective of the nature of the solute. We find that a constant offset with respect to the ice melting point curve, Deltaaw,het, can describe the observed freezing temperatures for each IN. Such a behavior is well-known for homogeneous ice nucleation from supercooled liquid droplets and has led to the development of water-activity-based ice nucleation theory. The large variety of investigated solutes together with different general types of ice nuclei studied (monolayers, ionic crystals, covalently bound network-forming compounds, and a mixture of chemically different crystallites) underlines the general applicability of water-activity-based ice nucleation theory also for heterogeneous ice nucleation in the immersion mode. Finally, the ice nucleation efficiencies of the various IN, as well as the atmospheric implication of the developed parametrization are discussed.
已使用四种不同的冰核（IN）进行了异质冰核化实验，即十九醇、二氧化硅、碘化银和亚利桑那试验粉尘。所有冰核均浸入液滴中或位于液滴表面。将这些冰核暴露于各种水溶液中，这些水溶液由硫酸铵、硫酸、氯化镁、氯化钠、氯化锂、硝酸钙、碳酸钾、醋酸钠、乙二醇、甘油、丙二酸、聚乙二醇300或氯化钠/丙二酸混合物组成。使用差示扫描量热仪和冷指池研究了冻结情况。结果表明，异质冰冻结温度随溶质浓度的增加而降低；然而，这种影响的程度取决于溶质。相比之下，当根据溶液水活度分析结果时，会出现非常一致的行为：所有四种冰核的异质冰核化温度都汇聚到一条单一曲线上，与溶质的性质无关。我们发现，相对于冰熔点曲线的恒定偏移量Δaw,het可以描述每个冰核观察到的冻结温度。这种行为在过冷液滴的均匀冰核化中是众所周知的，并导致了基于水活度的冰核化理论的发展。所研究的大量溶质以及所研究的不同一般类型的冰核（单层、离子晶体、共价键合的网络形成化合物以及化学性质不同的微晶混合物）强调了基于水活度的冰核化理论对于浸入模式下的异质冰核化也具有普遍适用性。最后，讨论了各种冰核的冰核化效率以及所开发参数化方法对大气的影响。
