Kaolinite particles as ice nuclei: learning from the use of different kaolinite samples and different coatings
Kaolinite particles as ice nuclei: learning from the use of different kaolinite samples and different coatings
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DOI：
10.5194/acp-14-5529-2014
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发表时间：
2014-06
影响因子：
6.3
通讯作者：
H. Wex;P. DeMott;Y. Tobo;S. Hartmann;Michael Rösch;T. Clauss;L. Tomsche;D. Niedermeier;F. Stratmann
中科院分区：
文献类型：
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作者：
H. Wex;P. DeMott;Y. Tobo;S. Hartmann;Michael Rösch;T. Clauss;L. Tomsche;D. Niedermeier;F. Stratmann
抽象的。对来自两个不同来源（Fluka 和粘土矿物协会 (CMS)）的高岭石颗粒作为冰核 (IN) 的能力进行了检查。这是在水不饱和状态下完成的，其中通常假设发生沉积冰成核，并且对于水过饱和条件，即浸入式冷冻模式。使用流管（莱比锡气溶胶云相互作用模拟器，LACIS）和连续流扩散室（CFDC）进行测量。使用纯的带涂层颗粒，涂层厚度为几纳米或更小，其中涂层由左旋葡聚糖、琥珀酸或硫酸组成。一般来说，发现涂层强烈减少沉积冰核。在水不饱和状态下形成的剩余冰可归因于浸入式冷冻，即颗粒浸入由涂层形成的浓缩溶液中。在浸入式冷冻模式下，两台仪器的冰成核率系数 jhet 彼此吻合良好，特别是考虑到仪器中的停留时间时。涂有左旋葡聚糖或琥珀酸的 Fluka 高岭石颗粒表现出与纯 Fluka 高岭石颗粒相同的 IN 活性；即，可以假设这两种类型的涂层不会化学改变冰活性表面，并且涂层在冰成核之前形成的液滴中被充分稀释，因此冰点降低可以忽略不计。然而，无论是涂有纯硫酸的 Fluka 高岭土颗粒，还是先涂有酸然后暴露于额外的水蒸气的 Fluka 高岭石颗粒，与纯颗粒相比，均显示出降低的冰成核能力。对于 CMS 高岭石颗粒，所有检查的颗粒（即纯颗粒和具有不同类型涂层的颗粒）在浸入式冷冻模式下使冰成核的能力相似。此外，CMS高岭石颗粒的jhet与涂有硫酸的Fluka高岭石颗粒的jhet相当。这表明 Fluka 高岭石具有一种冰成核表面特征，这种特征在 CMS 高岭石上不存在，并且可以通过与硫酸反应而被破坏。这可能是钾长石。
Abstract. Kaolinite particles from two different sources (Fluka and Clay Minerals Society (CMS)) were examined with respect to their ability to act as ice nuclei (IN). This was done in the water-subsaturated regime where often deposition ice nucleation is assumed to occur, and for water-supersaturated conditions, i.e., in the immersion freezing mode. Measurements were done using a flow tube (the Leipzig Aerosol Cloud Interaction Simulator, LACIS) and a continuous-flow diffusion chamber (CFDC). Pure and coated particles were used, with coating thicknesses of a few nanometers or less, where the coating consisted of levoglucosan, succinic acid or sulfuric acid. In general, it was found that the coatings strongly reduced deposition ice nucleation. Remaining ice formation in the water-subsaturated regime could be attributed to immersion freezing, with particles immersed in concentrated solutions formed by the coatings. In the immersion freezing mode, ice nucleation rate coefficients jhet from both instruments agreed well with each other, particularly when the residence times in the instruments were accounted for. Fluka kaolinite particles coated with either levoglucosan or succinic acid showed the same IN activity as pure Fluka kaolinite particles; i.e., it can be assumed that these two types of coating did not alter the ice-active surface chemically, and that the coatings were diluted enough in the droplets that were formed prior to the ice nucleation, so that freezing point depression was negligible. However, Fluka kaolinite particles, which were either coated with pure sulfuric acid or were first coated with the acid and then exposed to additional water vapor, both showed a reduced ability to nucleate ice compared to the pure particles. For the CMS kaolinite particles, the ability to nucleate ice in the immersion freezing mode was similar for all examined particles, i.e., for the pure ones and the ones with the different types of coating. Moreover, jhet derived for the CMS kaolinite particles was comparable to jhet derived for Fluka kaolinite particles coated with sulfuric acid. This is suggestive for the Fluka kaolinite possessing a type of ice-nucleating surface feature which is not present on the CMS kaolinite, and which can be destroyed by reaction with sulfuric acid. This might be potassium feldspar.