Nonanoic Acid Exhibits Inconsistency Between Bulk and Surface pKa

Thumbnail Image



Journal Title

Journal ISSN

Volume Title


Research Projects

Organizational Units

Journal Issue


Organic molecules at the ocean surface influence the climate through their reactions as coatings on sea spray aerosols, although many complex processes have not yet been fully described. By further characterizing molecules at this surface, climate effects through aerosol processes could be deduced. One common organic at the ocean surface is nonanoic acid (NA), which may be formed via the oxidation of oleic acid by gas phase species such as ozone. The pKa for an acid is characteristic and gives insight into its reactivity, but its value at the air-water interface is not necessarily the same as in bulk solution (~4.8 for many organic acids). The reactivity of sea-surface carboxylic acids cannot be well predicted without an accurate value of surface pKa. By varying pH via titration and simultaneously measuring the surface tension of a NA solution via a Wilhelmy platinum plate, the surface pKa of NA can be obtained. The surface pKa of NA would be shown on the titration curve of surface tension versus pH as the inflection point. At pH 12, NA is ionized and its surface tension is 70.68 mN/m, near that of neat water (72.80 mN/m). At pH 3, the surface tension of NA is 30.49 mN/m, showing an increase in surface activity. Additionally, Brewster angle microscopy (BAM) will be used in the future to image NA at the surface at different pH values. With an accurate pKa and visual evidence of the surface activity of nonanoic acid, the atmospheric impact of aerosols could be further described. Investigation of this inconsistency is a first step to better predict climate change.


Mathematical and Physical Sciences (The Ohio State University Spring Undergraduate Research Expo)


Chemistry, Atmospheric, Surface, pKa, Aerosol