Active sites for ice nucleation differ depending on nucleation mode.
Active sites for ice nucleation differ depending on nucleation mode.
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DOI：
10.1073/pnas.2022859118
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发表时间：
2021-05-04
影响因子：
11.1
通讯作者：
Christenson HK
中科院分区：
文献类型：
--
作者：
Holden MA;Campbell JM;Meldrum FC;Murray BJ;Christenson HK
大气中冰晶的出现是地球气候的重要组成部分。冰晶通常形成在悬浮在大气中的固体颗粒上，其中水滴可以在颗粒上凝结然后冻结，或者冰可以直接在颗粒上生长而没有水首先凝结。然而，对于为什么某些类型的颗粒特别有效的理解却很差。在这里，我们使用显微镜来识别冰首先在大气中重要的矿物上形成的地点，并发现两种冰生长模式之间的显着差异。这些结果提供了深入了解的因素，管理在大气中的冰的形成，并暗示在指导晶体形成的表面形态的重要作用。尽管对我们地球的气候至关重要，但人们对云中冰晶的成核作用知之甚少。成核主要发生在罕见的“活性位点”目前在空气中的颗粒，如矿物粉尘，但成核途径是不同的气象条件下。这些产生两个关键的成核途径，其中颗粒或者浸没在过冷的液态水滴中（浸没冷冻模式）或者悬浮在过饱和蒸气中（沉积模式）。然而，目前还不清楚，如果相同的活性位点负责在这两种模式的成核。在这里，我们直接比较的网站，是活跃在这两种模式下进行浸泡冻结和沉积实验的两个大气中重要的矿物（长石和石英）的相同的薄切片。对于这两种基板，我们确认，成核是由有限数量的网站和显示，有两组网站之间的相关性很小，在每个实验方法操作：在这两种材料，只有6个73个网站的浸没冷冻成核活跃也活跃的沉积成核。显然，不同的属性决定了每种模式的成核位点的活性，我们使用的孔冷凝和冻结的概念，认为有效的沉积位点的大小和/或几何形状的要求不相关的有效的浸泡冻结网站。因此，成核的能力是路径依赖的，并且在云模型中应用实验数据时必须明确考虑成核模式。
The appearance of ice crystals in the atmosphere is an important component of our planet’s climate. Ice crystals usually form on solid particles suspended in the atmosphere, where a water droplet can either condense on the particle and then freeze, or ice can grow directly on the particle without water first condensing. However, understanding of why some types of particles are especially effective is poor. Here, we use microscopy to identify the sites where ice first forms on atmospherically important minerals and find a significant difference between the two modes of ice growth. These results provide insight into the factors that govern ice formation in the atmosphere and imply an important role of surface morphology in directing crystal formation. The nucleation of ice crystals in clouds is poorly understood, despite being of critical importance for our planet’s climate. Nucleation occurs largely at rare “active sites” present on airborne particles such as mineral dust, but the nucleation pathway is distinct under different meteorological conditions. These give rise to two key nucleation pathways where a particle is either immersed in a supercooled liquid water droplet (immersion freezing mode) or suspended in a supersaturated vapor (deposition mode). However, it is unclear if the same active sites are responsible for nucleation in these two modes. Here, we directly compare the sites that are active in these two modes by performing immersion freezing and deposition experiments on the same thin sections of two atmospherically important minerals (feldspar and quartz). For both substrates, we confirm that nucleation is dominated by a limited number of sites and show that there is little correlation between the two sets of sites operating in each experimental method: across both materials, only six out of 73 sites active for immersion freezing nucleation were also active for deposition nucleation. Clearly, different properties determine the activity of nucleation sites for each mode, and we use the pore condensation and freezing concept to argue that effective deposition sites have size and/or geometry requirements not of relevance to effective immersion freezing sites. Hence, the ability to nucleate is pathway dependent, and the mode of nucleation has to be explicitly considered when applying experimental data in cloud models.
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DOI：
10.1175/amsmonographs-d-16-0006.1
发表时间：
2017-01-01
期刊：
ICE FORMATION AND EVOLUTION IN CLOUDS AND PRECIPITATION: MEASUREMENT AND MODELING CHALLENGES
影响因子：
--
作者：
Kanji, Zamin A.;Ladino, Luis A.;Kraemer, Martina
通讯作者：
Kraemer, Martina
影响因子：
6.3
作者：
Harrison, Alexander D.;Lever, Katherine;Murray, Benjamin J.
通讯作者：
Murray, Benjamin J.
影响因子：
4
作者：
Mehlhorn, Michael;Schnur, Sebastian;Morgenstern, Karina
通讯作者：
Morgenstern, Karina
影响因子：
8.6
作者：
Campbell, James M.;Christenson, Hugo K.
通讯作者：
Christenson, Hugo K.
影响因子：
3.1
作者：
Christenson, Hugo K.
通讯作者：
Christenson, Hugo K.