There exists large uncertainty in the literature as to the pK of medium-chain fatty acids at the air-water interface. Via surface tension titration, the surface-pK values of octanoic (C), nonanoic (C), and decanoic (C) fatty acids are determined to be 4.9, 5.8, and 6.4, respectively. The surface-pK determined with surface tension differs from the bulk value obtained during a standard acid-base titration. Near the surface-pK of the C and C systems, surface tension minima are observed and are attributed to the formation of surface-active acid-soap complexes. The direction of the titration is shown to affect the surface-pK of the C system, as the value shifts to 5.2 with NaOH titrant due to a higher concentration of Na ions at pH values close to the surface-pK. As the reactivity and climate-relevant properties of sea spray aerosols (SSA) are partially dictated by the charge and surface activity of the organics at the aerosol-atmosphere interface, the results presented here on SSA-identified C-C fatty acids can be used to better predict the health and climate impact of particles with significant concentrations of medium-chain fatty acids.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.