Environ. Sci. Technol. 2009, 43, 5152–5154
Response to Comment on “Experimental pKa Determination for Perfluorooctanoic Acid (PFOA) and the Potential Impact of pKa Concentration Dependence on Laboratory-Measured Partitioning Phenomena and Environmental Modeling” Goss and Arp (1) critically analyze aspects of three recent publications (2-4) but are mistaken in their analysis. Concerning the Role of the Surface Microlayer in PFOA Water-Air Transfer. Goss and Arp question the existence of a mechanism for aerosol-mediated water-air PFOA partitioning and the acidity of water at the air-water interface: “...the postulated increased protonation of PFO/ PFOA (or other bases) in the surface layer as compared to the bulk layer and the inferred mechanistic explanation for the water surface-air transfer cannot exist” (1). They rely on the supposition that we are mistaken concerning the pH of the surface microlayer. However, PFO will always coexist with PFOA regardless of the pH. Regarding the pH of the surface, Buch et al. and Va´cha et al. (for which Jungwirth is a coauthor) state the following, “...the H2O surface is predicted to be acidic with pH
