We use synchrotron based x-ray photoelectron spectroscopy (XPS) experiments to study the composition and chemistry at the liquid/vapor interface of aqueous solutions. These experiments are motivated by an interest in the fundamental behavior of aqueous interfaces as well as applications to aqueous aerosols in the atmosphere. We take advantage of the variable energy characteristic of synchrotron radiation to carry out XPS experiments as a function of experimental probing depth, thereby generating a depth profile of the liquid/vapor interface. Recent experiments in which we have studied the composition of aqueous salt solutions in the presence of organic surfactants will be described. In addition, studies of acid/base equilibria at the liquid/vapor interface will be described. Our depth profile experiments show that the acid/base equilibrium at the solution surface is modified by the differences in bulk solubility of the acid and base involved in the equilibrium. Two different experimental approaches have been used: an ambient pressure end station at the Advanced light source is equipped with a differentially pumped electron energy analyzer allowing studies with the sample chamber at pressures of a few torr. This system has been used to study saturated aqueous solutions of alkali halide salts. A liquid/jet endstation at the BESSY synchrotron has allowed us to study the surface segregation of molecular ions such as nitrate in aqueous solutions as a function of solution concentrations.