The study challenges the conventional view that larger ions are surface-active at the air/water interface, suggesting instead that ions in typical electrolyte solutions are located in a subsurface region. This finding leads to a stratification of the interface into two distinct water layers: an outermost ion-depleted surface and a subsurface ion-enriched layer. The authors use high-level heterodyne-detected vibrational sum-frequency generation (HD-VSFG) and neural network-assisted ab initio molecular dynamics (AIMD) simulations to investigate the structure of ten electrolyte solutions. They show that the formation of an electric double layer (EDL) cannot fully explain the observed HD-VSFG spectra, except for HCl and NaClO3. The results highlight that the conventional classification of ions' surface propensity as either 'surface enriched' or 'surface depleted' is overly simplistic, and provide a more accurate understanding of the interfacial structure of typical electrolyte solutions. The study also demonstrates the utility of HD-VSFG in probing the molecular-level details of liquid surfaces, contributing to the development of environmental models and the understanding of complex interfaces in various applications.The study challenges the conventional view that larger ions are surface-active at the air/water interface, suggesting instead that ions in typical electrolyte solutions are located in a subsurface region. This finding leads to a stratification of the interface into two distinct water layers: an outermost ion-depleted surface and a subsurface ion-enriched layer. The authors use high-level heterodyne-detected vibrational sum-frequency generation (HD-VSFG) and neural network-assisted ab initio molecular dynamics (AIMD) simulations to investigate the structure of ten electrolyte solutions. They show that the formation of an electric double layer (EDL) cannot fully explain the observed HD-VSFG spectra, except for HCl and NaClO3. The results highlight that the conventional classification of ions' surface propensity as either 'surface enriched' or 'surface depleted' is overly simplistic, and provide a more accurate understanding of the interfacial structure of typical electrolyte solutions. The study also demonstrates the utility of HD-VSFG in probing the molecular-level details of liquid surfaces, contributing to the development of environmental models and the understanding of complex interfaces in various applications.