Ice Nucleation Insights: Interfacial Electric Fields and Fatty Alcohol and Acid Hydration
Abstract
Sea spray aerosol composition contributes to cloud and ice formation in our atmosphere. It has been shown that sea spray aerosols containing fatty acid can aid ice nucleation at higher temperatures, such as -28 oC, instead of the traditional freezing at -36 oC in which pure crystalline phases are present. Our study seeks to derive the chemical and physical mechanisms which drive increased ice nucleating efficiency of these fatty acids and other biogenic constituent classes such as fatty alcohols. Long chain fatty alcohols are often effective ice nucleators. The fatty alcohol headgroup lattice packing better templates ice, at higher temperatures, relative to fatty acids. However, the mechanistic process behind this templating is not very well understood. Information on the hydration and electric effects is paramount in our understanding of water templating as it provides important insights regarding ice nucleation. Here we used interface-sensitive infrared reflection-absorption spectroscopy (IRRAS) and surface pressure and potential area isotherms to reveal a hydrophilic hydration effect by investigating and C18 fatty acid and alcohol. A large enhancement in surface potential of the long-chain fatty alcohol monolayer was observed, suggesting increased ordering relative to the surface normal. Surprisingly, analysis of the -OH stretching features in the IRRAS spectra showed remarkably similar 1st hydration shell signatures for the alcohol -OH moiety and carboxylic acid head group, contrary to their significant chemical differences. Our observations indicate that both fatty acids and fatty alcohols exhibit change of the 4-coordinate water structure, explained by extended water network perturbation. This suggests that the headgroups also perturb the waters in the 2nd hydration shell, as well. Understanding and predicting the evolution of ice phase-change in our atmosphere is a phenomenon still in need of further investigation. However, our study helps to unravel the molecular complexity of sea spray aerosols by clarifying the role of fatty acids and fatty alcohols in heterogeneous ice nucleation due to its integral influence on tropospheric composition, hydrological cycle, and cloud lifetime.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMA035.0009V
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0312 Air/sea constituent fluxes;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0315 Biosphere/atmosphere interactions;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES