Dilute aqueous solutions of the atmospheric organic surfactant sodiumdecanoate have been studied using surface sensitive X-ray photoelectronspectroscopy combined with synchrotron radiation. We studied thedecanoate/decanoic acid speciation and preferential adsorption at thevapor–liquid interface, and the responses to mixing in solution with some ofthe most common atmospheric inorganic ions, Na, NH, Cl, andSO. We observe little orno influence of Na, Cl, orSO ions, on neither the relative speciation nor theindividual adsorption properties of decanoate and decanoic acid. Inparticular, no significant salting-out effect due to common Nacations of the organic and inorganic salts was observed for these solutions.On the other hand, mixing with NH cations resulted in a pronouncedsurface enhancement of decanoic acid, which is attributed to surface specificacid–base chemistry. These changes in surface/bulk partitioning and surfacespeciation may significantly affect properties of aqueous droplets containingdecanoate/decanoic acid, and potential implications for several processescritical to the climate effects of atmospheric aerosols are discussed.
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