Display omitted ► Glancing-angle Raman scattering probed the surface of nitrate-containing solutions. ► The extent of nitric acid dissociation in the surface region is similar to that in the bulk. ► We obtained an adsorption isotherm for nitrate to the aqueous surface. ► Nitrate exhibits near neutral surface activity. Glancing-angle Raman spectra of aqueous KNO3 and HNO3 solutions were used to determine the degree of nitric acid dissociation, α, in the bulk and in the surface region. Our results suggest that α in the surface region is similar to that in the bulk and highlight the importance of water molecule availability to the dissociation process. Using the α’s and the ν-symNO3- Raman intensities, we obtained an adsorption isotherm for NO3- to the surface region from which we calculated a Kads, of 0.19±0.03Lmol−1, implying that nitrate exhibits an almost neutral surface affinity.