Active sites for ice nucleation differ depending on nucleation mode
| Autor: | James M. Campbell, Hugo K. Christenson, Fiona C. Meldrum, Mark A. Holden, Benjamin J. Murray |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2021 |
| Předmět: |
Supersaturation
Multidisciplinary Ice crystals crystallization nucleation Condensation Nucleation ice F750 Physics::Geophysics Earth Atmospheric and Planetary Sciences Chemical physics pores Physical Sciences active sites Ice nucleus Particle Deposition (phase transition) Astrophysics::Earth and Planetary Astrophysics Supercooling human activities Physics::Atmospheric and Oceanic Physics |
| Zdroj: | Proceedings of the National Academy of Sciences of the United States of America |
| ISSN: | 0027-8424 |
| Popis: | Significance 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. |
| Databáze: | OpenAIRE |
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