The molecular structure of the interfacial regions of aqueous electrolytes is 
poorly understood, despite its crucial importance in many biological, 
technological, and atmospheric processes. A long-term controversy pertains 
between the standard picture of an ion-free surface layer and the strongly ion 
specific behavior indicating in many cases significant propensities of simple 
inorganic ions for the interface. Here, we present a unified and consistent 
view of the structure of the air/solution interface of aqueous electrolytes 
containing monovalent inorganic ions. Molecular dynamics calculations show 
that in salt solutions and bases the positively charged ions, such as alkali 
cations, are repelled from the interface, while the anions, such as halides or 
hydroxide, exhibit a varying surface propensity, correlated primarily with the 
ion polarizability and size. The behavior of acids is different due to a 
significant propensity of hydronium cations for the air/solution interface. 
Therefore, both cations and anions exhibit enhanced concentrations at the 
surface and, consequently, these acids (unlike bases and salts) reduce the 
surface tension of water. The results of the simulations are supported by 
surface selective non-linear vibrational spectroscopy, which reveals among 
other things that the hydronium cations are present at the air/solution 
interface. The ion specific propensities for the air/solution interface have 
important implications for a whole range of heterogeneous physical and 
chemical processes, including atmospheric chemistry of aerosols, corrosion 
processes, and bubble coalescence.