Homogeneous ice freezing temperatures and ice nucleation rates of aqueous ammonium sulfate and aqueous levoglucosan particles for relevant atmospheric conditions.
Homogeneous ice freezing temperatures and ice nucleation rates of aqueous ammonium sulfate and aqueous levoglucosan particles for relevant atmospheric conditions.
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相关大气条件下硫酸铵水溶液和左旋葡聚糖水溶液颗粒的均匀冰冻温度和冰成核速率。
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发表时间：
2009
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通讯作者：
Miguel David Lopez
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作者：
D. Knopf;Miguel David Lopez
采用光学显微镜技术研究了微米级水性 (NH4)2SO4 和水性左旋葡聚糖颗粒的均质冰成核。引入了一种新的实验方法，使我们能够控制水滴的初始水活度。测定这些直径为 10 至 80 微米的水溶液液滴的均匀冰冻结温度和冰融化温度。浓度为 5-39 wt% 的水性 (NH4)2SO4 颗粒和初始水活度为 0.85-0.99 的水性左旋葡聚糖颗粒的均质冰成核产生的均质冰成核速率系数上限高达 1x10(10) cm(-3) s(-1)。将实验得出的均质冰冻结温度和均质冰成核率系数的上限与基于水分活度的冰成核理论的相应预测进行了比较[T. Koop、B. P. Luo、A. Tsias 和 T. Peter，《自然》，2000, 406, 611]。研究发现，基于水活度的冰成核理论可以捕获实验得出的水性 (NH4)2SO4 和水性左旋葡聚糖颗粒的冰冻结温度和均质冰成核速率系数。然而，实验得出的值和预测值之间的一致性程度，特别是均匀冰成核率系数，关键取决于在相应冰冻温度下获得水活度的外推方法。研究表明，与单独观测均质冰冻结温度相比，实验得出的冰冻结温度和均质冰成核速率系数的组合可以更好地验证基于水分活度的冰成核理论。简要讨论了基于水活性的冰成核理论的应用和最大冰粒生成速率的推导对大气的影响。
Homogeneous ice nucleation from micrometre-sized aqueous (NH4)2SO4 and aqueous levoglucosan particles is studied employing the optical microscope technique. A new experimental method is introduced that allows us to control the initial water activity of the aqueous droplets. Homogeneous ice freezing temperatures and ice melting temperatures of these aqueous solution droplets, 10 to 80 microm in diameter, are determined. Homogeneous ice nucleation from aqueous (NH4)2SO4 particles 5-39 wt% in concentration and aqueous levoglucosan particles with initial water activities of 0.85-0.99 yield upper limits of the homogeneous ice nucleation rate coefficients of up to 1x10(10) cm(-3) s(-1). The experimentally derived homogeneous ice freezing temperatures and upper limits of the homogeneous ice nucleation rate coefficients are compared with corresponding predictions of the water-activity-based ice nucleation theory [T. Koop, B. P. Luo, A. Tsias and T. Peter, Nature, 2000, 406, 611]. It is found that the water-activity-based ice nucleation theory can capture the experimentally derived ice freezing temperatures and homogeneous ice nucleation rate coefficients of the aqueous (NH4)2SO4 and aqueous levoglucosan particles. However, the level of agreement between experimentally derived and predicted values, in particular for homogeneous ice nucleation rate coefficients, crucially depends on the extrapolation method to obtain water activities at corresponding freezing temperatures. It is suggested that the combination of experimentally derived ice freezing temperatures and homogeneous ice nucleation rate coefficients can serve as a better validation of the water-activity-based ice nucleation theory than when compared to the observation of homogeneous ice freezing temperatures alone. The atmospheric implications with regard to the application of the water-activity-based ice nucleation theory and derivation of maximum ice particle production rates are briefly discussed.