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Chemistry at the surfaces of liquids and solutions is of great importance to a wide range of problems. In particular, interfacial chemistry of aqueous solutions is important in environmental sciences. However, little is known in detail about the composition of the liquid/vapor interface relative to that of bulk solutions. We have used ambient pressure photoelectron spectroscopy at the ALS synchrotron light source to study the composition of the liquid/vapor interface of aqueous salt solutions in contact with equilibrium water vapor pressures. Our results show that larger, more polarizable anions are enhanced at the interface in contrast to less polarizable anions such as fluoride, which is repelled from the interface. We have also studied the impact on the interfacial composition of the addition of an organic surfactant (e.g., butanol) to the solution. In addition, we will discuss the use of ambient pressure XPS to follow the oxidation of potassium iodide both without water and at water pressures up to a few torr—which is sufficient to provide ionic mobility at the salt surface. Each of these studies involves a combination of XPS experiments and MD simulations of the aqueous solution interface. Our results will be discussed in the context of implications for environmental chemistry. |