Peckhaus Andreas, Kiselev Alexei, Wagner Robert, Duft Denis, Leisner Thomas
Atmospheric Aerosol Research Department, Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz pl. 1, Eggenstein-Leopoldshafen 76344, Germany.
Atmospheric Aerosol Research Department, Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz pl. 1, Eggenstein-Leopoldshafen 76344, GermanyInstitute of Environmental Physics, Heidelberg University, Im Neuenheimer Feld 229, Heidelberg, Germany.
J Chem Phys. 2016 Dec 28;145(24):244503. doi: 10.1063/1.4972589.
Recent laboratory studies indicate that the hydrated form of crystalline NaCl is potentially important for atmospheric processes involving depositional ice nucleation on NaCl dihydrate particles under cirrus cloud conditions. However, recent experimental studies reported a strong discrepancy between the temperature intervals where the efflorescence of NaCl dihydrate has been observed. Here we report the measurements of the volume specific nucleation rate of crystalline NaCl in the aqueous solution droplets of pure NaCl suspended in an electrodynamic balance at constant temperature and humidity in the range from 250 K to 241 K. Based on these measurements, we derive the interfacial energy of crystalline NaCl dihydrate in a supersaturated NaCl solution and determined its temperature dependence. Taking into account both temperature and concentration dependence of nucleation rate coefficients, we explain the difference in the observed fractions of NaCl dihydrate reported in the previous studies. Applying the heterogeneous classical nucleation theory model, we have been able to reproduce the 5 K shift of the NaCl dihydrate efflorescence curve observed for the sea salt aerosol particles, assuming the presence of super-micron solid inclusions (hypothetically gypsum or hemihydrate of CaSO). These results support the notion that the phase transitions in microscopic droplets of supersaturated solution should be interpreted by accounting for the stochastic nature of homogeneous and heterogeneous nucleation and cannot be understood on the ground of bulk phase diagrams alone.
最近的实验室研究表明，结晶态氯化钠的水合形式对于涉及在卷云条件下二水合氯化钠颗粒上沉积冰核形成的大气过程可能具有重要意义。然而，最近的实验研究报告称，观察到二水合氯化钠风化的温度区间存在很大差异。在此，我们报告了在250 K至241 K的恒定温度和湿度下，悬浮在电动天平中的纯氯化钠水溶液滴中结晶态氯化钠的体积比成核速率的测量结果。基于这些测量结果，我们推导了过饱和氯化钠溶液中二水合结晶态氯化钠的界面能，并确定了其温度依赖性。考虑到成核速率系数的温度和浓度依赖性，我们解释了先前研究中报道的二水合氯化钠观察分数的差异。应用非均相经典成核理论模型，假设存在超微米固体夹杂物（假设为石膏或硫酸钙半水合物），我们能够重现海盐气溶胶颗粒观察到的二水合氯化钠风化曲线5 K的偏移。这些结果支持这样一种观点，即过饱和溶液微观液滴中的相变应通过考虑均相和非均相成核的随机性来解释，而不能仅基于体相图来理解。
