Simulating atmospheric freezing of single aqueous droplets to ice in a cryogenically cooled ultrasonic levitator

• 成果类型: Article
• 署名作者: Biswas, Souvick; Paul, Dababrata; Mondal, Koushik; Kaiser, Ralf I.
• 署名单位: University of Hawaii System; University of Hawaii Manoa
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-11774
• DOI: 10.1073/pnas.242554312
• 发表日期: 2025-02-11
• 关键词: water; surface

摘要

Atmospheric freezing of water droplets suspended in air followed by cloud formation and precipitation represent fundamental steps of the terrestrial water cycle. These aqueous droplets exhibit distinct freezing mechanisms and thermodynamic requirements com-pared to bulk water often forming metastable supercooled water at subzero temperatures on the Celsius scale (<273 K) prior to crystallization. Here, we report on a real- time spectroscopic investigation combined with simultaneous visualizations of single aque-ous droplet freezing events inside a cryogenically cooled ultrasonic levitation chamber with the ultimate goal of probing the molecular structure evolution and stages of ice formation. The observed droplet freezing follows a pseudoheterogeneous ice nucleation mechanism mimicking the process that occurs for atmospherically supercooled water droplets at the air-water interface. This proof- of- concept experimental setup allows future crystallization studies of homo- and heterogeneously doped aqueous droplets under simulated atmospheric environments-also in the presence of reactive trace gases, thus untangling dynamic molecular interactions and chemical reactions, which are of fundamental interest to low- temperature atmospheric chemistry delineating with ice nucleation mechanisms.