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DY: Fachverband Dynamik und Statistische Physik

DY 20: Focus Session: Water – from Atmosphere to Space I (joint session CPP/DY)

DY 20.2: Vortrag

Dienstag, 10. März 2026, 10:00–10:15, ZEU/LICH

The Effect of pH on the Structure of Model Sea Spray Aerosol Surfaces — •Clara M. Saak, Lars Höhner, and Ellen H.G. Backus — Institute of Physical Chemistry, Faculty of Chemistry, University of Vienna, Währinger Straße 42, 1090 Vienna, Austria

Aerosols play a key role in the global climate due to their ability to scatter and reflect solar radiation and to act as cloud condensation nuclei (CCN), exerting a pronounced cooling influence on the global climate. In particular, the surface availability of ions and organic compounds is known to affect the hygroscopicity of the particle and thereby its ability to act as a CCN [1]. While the surface propensity of individual compounds has been studied widely, much less is known about more complex systems. Here we focus on the impact of bulk pH on the architecture of mixed aqueous interfaces. In atmospheric systems the pH has been shown to range from roughly pH 8 to 2 [2]. Using sum-frequency-generation (SFG) spectroscopy in conjunction with surface tension data we study the surface composition and structure of short and long chain organic acids at different protonation stages, obtained by varying the pH. Using this approach, we find pronounced changes in the structuring of the aqueous sub-surface layers depending on the specific composition and pH, and in the Gibbs free energy of adsorption of the studied organics. Our results show that it is feasible for subtle environmental changes to considerably affect structure and composition of the aqueous interface, which is known to play a key role in aerosol hygroscopicity. [1] Zieger, Nat. Commun. 2017, 8, 15883. [2] Angle, PNAS, 2021, 118, 2, e2018397118

Keywords: Aqueous Aerosol; Sum-frequency-generation (SFG) Spectroscopy; Surface structure; pH dependence; Cloud Nucleation