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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 19: Focus Session: Water – from Atmosphere to Space I (joint session CPP/DY)

CPP 19.1: Topical Talk

Dienstag, 10. März 2026, 09:30–10:00, ZEU/LICH

Surface adsorption and protonation equilibrium of atmospheric organics at the aqueous surface — •Nønne Prisle — Center for Molecular Water Science, Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany — Institute of Inorganic and Applied Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany — Center for Atmospheric Research, University of Oulu, P.O. Box 4500, FI-90014, Oulu, Finland

Atmospheric aerosols comprise a significant fraction of organic species which frequently exhibit both surface activity and Brönsted acidity or basicity in aqueous solutions. The high surface area to bulk volume ratios of nano- and microscopic aerosols and droplets further favor surface-specific states, affecting both bulk-phase and heterogeneous chemistry.

We used X-ray Photoelectron Spectroscopy (XPS) in combination with high-brilliance synchrotron radiation to directly observe the protonation state of atmospheric acids and bases at the surfaces of aqueous aerosol and droplet models. We found that for each acid-base pair, the neutral species is enhanced in the surface, consistent with its higher surface activity, compared to the charged conjugate. This introduces a shift in the protonation equilibrium at the aqueous surface corresponding to an apparent change in pKa of 1-2 pH units, depending on the concentration, acidity, and surface activity of the conjugate acidic and basic species.

Keywords: water; surfactants; aerosols; atmosphere; climate