The chemical and physical nature of the gas/aerosol particle interface is incredibly important to atmospheric chemistry as well as global health. Increased ion activity, acidity, viscosity light scattering, and molecular ordering at the gas/aerosol particle interface have led to numerous investigations into this system and its effects on larger systems.  Here we present the in situ, interface specific, observation and characterization of carboxylic acid species at the gas/aerosol particle interface through vibrational sum frequency scattering (VSFS) spectroscopy. In situ VSFS in combination with simultaneous hyper-Raman scattering (HRS) spectroscopy of the underlying in-particle phase allows direct investigation of the vibrational characteristics of laboratory- generated aqueous aerosol particles containing formic and acetic acids as they float in the air. Additionally, we demonstrate interfacial differences between the curved gas/aerosol particle and planar air/liquid interfaces, elucidating flaws in the assumption that the two are interchangeable. The sensitivity of VSFS to probe the gas/aerosol particle interface with few-particle density at ambient conditions offers a unique approach to the study of environmentally and biologically relevant atmospheric and viral aerosols.

In situ characterization of carboxylic acid apecies at the gas/aerosol particle interface through vibrational sum frequency scattering spectroscopy

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ACS Fall 2022

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