Model Behavior: Characterization of Hydroxyacetone at the Air-Water Interface Using Experimental and Computational...

Area of Science:

• Atmospheric Chemistry
• Physical Chemistry
• Surface Science

Background:

• Small atmospheric aldehydes and ketones significantly influence secondary organic aerosol (SOA) formation.
• Many such compounds are difficult to study due to hydration and oligomerization.
• Hydroxyacetone (HA) is a notable exception, predominantly existing in its unhydrated monomeric form, making it a valuable model for SOA research.

Purpose of the Study:

• To investigate the surface behavior of hydroxyacetone (HA) at the air-water interface.
• To understand the molecular ordering and interactions of HA at interfaces.
• To elucidate the implications of HA's interfacial behavior on its role in atmospheric SOA formation.

Main Methods:

• Vibrational sum frequency (VSF) spectroscopy to probe molecular structure and orientation.
• Wilhelmy plate surface tensiometry to measure surface activity.
• Computational molecular dynamics (MD) simulations and density functional theory (DFT) calculations for theoretical insights.

Main Results:

• Hydroxyacetone (HA) exhibits significant surface activity and ordering at the air-water interface.
• Oriented water molecules are present at the interface, even at high HA concentrations.
• Both cis and trans HA conformers are detected at the interface with distinct orientations, influenced by depth (surface vs. subsurface).

Conclusions:

• The air-water interface is dynamically ordered, comprising multiple HA conformers and solvated water.
• HA's distinct interfacial behavior, including its ordering and the presence of oriented water, impacts its behavior in atmospheric aqueous particles.
• Understanding these interfacial properties is crucial for accurately modeling HA's contribution to SOA formation.