Solvation of surface-active tetrabutyl-ammonium iodide (TBAI) in pure liquid water and in sodium bromide aqueous solution was investigated by photoelectron spectroscopy and by molecular dynamics simulations. Using VUV synchrotron radiation the experimental technique is particularly suitable to investigate the solution surface. The observed anion signal intensity changes in the photoemission spectra, in the presence of bromide, are consistent with the varying propensities of the different ions for the solution interface, analyzed in terms of hydrophobic, polarization, and ion-ion interactions. While the cations are surface-bound due to hydrophobic interactions, the anions are driven to the vacuum/solution interface by their large polarizability and size. Iodide is more polarizable, and hence more surface-active than the smaller bromide, which explains the relatively small decrease of the iodide photoemission signal when TBAI is dissolved in bromide aqueous solution.