Molecular dynamics simulations with polarizable interactions were carried out to investigate how cation charge and ion pairing influence the anion propensity for the air-water interface of water. Higher cation charge resulted in greater interfacial activity for chloride, along with stronger NaCl binding. It was also found that artificially weakening NaCl interactions without changing charge has only a minor influence on chloride interfacial activity. Furthermore, we found that for a single NaCl contact ion pair in water that it had a much lower interfacial free energy than chloride alone, showing that the presence of a cation enhances anion interfacial activity. (C) 2010 Published by Elsevier B.V.