“…For most aqueous solutions containing multiple species, it is currently not known whether the observed surface enhancement is due to differences in the density profiles of the various species or competition for limited surface sites between species with different surface propensities (Prisle et al, 2012;Werner et al, 2014Werner et al, , 2018O ¨hrwall et al, 2015). It is possible to derive relative density profiles using angular-resolved XPS, as demonstrated for solutions containing environmental organic compounds (Dupuy et al, 2022(Dupuy et al, , 2023, and in particular organosulfates (Lewis et al, 2019). For these mixtures, the relative surface abundances of co-solutes observed with XPS was found to originate from different peak intensity, rather than peak depth, of the radial density profiles with respect to the surface.…”