Nachbar Mario, Duft Denis, Leisner Thomas
Institute of Environmental Physics , University of Heidelberg , Im Neuenheimer Feld 229 , 69120 Heidelberg , Germany.
Institute of Meteorology and Climate Research , Karlsruhe Institute of Technology-KIT , P.O. Box 3640, 76021 Karlsruhe , Germany.
J Phys Chem B. 2018 Nov 1;122(43):10044-10050. doi: 10.1021/acs.jpcb.8b06387. Epub 2018 Oct 19.
Amorphous solid water is probably the most abundant form of solid water in the universe. Its saturation vapor pressure and thermodynamic properties, however, are not well known. We have investigated the saturation vapor pressure over vapor-deposited amorphous ice at temperatures between 133 and 147 K using a novel experimental method. The new method determines the absolute vapor pressures and the sublimation rates by measuring the mass growth rates of ice-covered nanoparticles under supersaturated water vapor conditions. We find that the vapor pressure of amorphous solid water is up to a factor of 3 higher than that predicted by current parameterizations, which are based in part on calorimetric measurements. We demonstrate that the calorimetric measurements can be reconciled with our data by acknowledging the formation of nanocrystalline ice as an intermediate ice phase during the crystallization of amorphous ice. As a result, we propose a new value for the enthalpy of crystallization of amorphous solid water of Δ H = 2312 ± 227 J/mol, which is about 1000 J/mol higher than the current consensus. Our results shine a new light on the abundance of water ice clouds on Mars and mesospheric clouds on Earth and may alter our understanding of ice formation in the stratosphere.
非晶态固体水可能是宇宙中最丰富的固体水形式。然而，其饱和蒸气压和热力学性质尚不为人所知。我们使用一种新颖的实验方法，研究了在133至147 K温度范围内气相沉积非晶冰上的饱和蒸气压。这种新方法通过测量过饱和水蒸气条件下覆冰纳米颗粒的质量增长率来确定绝对蒸气压和升华速率。我们发现，非晶态固体水的蒸气压比目前部分基于量热测量的参数化预测值高出多达3倍。我们证明，通过承认在非晶冰结晶过程中形成纳米晶冰作为中间冰相，量热测量结果可以与我们的数据相协调。因此，我们提出非晶态固体水结晶焓的新值为ΔH = 2312 ± 227 J/mol，这比目前的共识值高出约1000 J/mol。我们的研究结果为火星上的水冰云以及地球上中层大气云的丰度提供了新的线索，并可能改变我们对平流层中冰形成的理解。
