Abstract
Abstract. Dilute aqueous solutions of the atmospheric organic surfactant sodium decanoate have been studied using surface sensitive X-ray photoelectron spectroscopy combined with synchrotron radiation. We studied the decanoate/decanoic acid speciation and preferential adsorption at the vapor–liquid interface, and the responses to mixing in solution with some of the most common atmospheric inorganic ions, Na+, NH4+, Cl−, and SO42−. We observe little or no influence of Na+, Cl−, or SO42− ions, on neither the relative speciation nor the individual adsorption properties of decanoate and decanoic acid. In particular, no significant salting-out effect due to common Na+ cations of the organic and inorganic salts was observed for these solutions. On the other hand, mixing with NH4+ cations resulted in a pronounced surface enhancement of decanoic acid, which is attributed to surface specific acid–base chemistry. These changes in surface/bulk partitioning and surface speciation may significantly affect properties of aqueous droplets containing decanoate/decanoic acid, and potential implications for several processes critical to the climate effects of atmospheric aerosols are discussed.
Highlights
Aerosol effects still constitute the greatest uncertainties in assessing anthropogenic contributions to global climate change (IPCC, 2007)
The measured spectra are presented in two separate figures due to experimental conditions; for the spectra in Fig. 2, alignment of the X-ray photoelectron spectroscopy (XPS) setup was maintained between the individual experiments presented in each panel and the recorded photoelectron signal intensities can be immediately compared
We have characterized the surfaces of dilute binary aqueous solutions of the organic surfactant sodium decanoate, and ternary mixtures of sodium decanoate with four different inorganic salts, sodium chloride, ammonium sulfate, sodium sulfate, and ammonium chloride, using synchrotron based Xray photoelectron spectroscopy (XPS)
Summary
Aerosol effects still constitute the greatest uncertainties in assessing anthropogenic contributions to global climate change (IPCC, 2007) Both direct and indirect climate effects of atmospheric aerosol particles are governed by their numbers, sizes, and chemical properties. As well as effects of mutual interactions between individual particle components within the aqueous phase, is essential to considerations of atmospheric aerosol properties. Describing such interactions poses many challenges yet to be met, owing to the vast number of chemical species and the wide ranges of their concentrations and relative mixing states observed in the atmosphere, just as the miniscule amounts of material present in submicrometer aerosols prevent direct observations of many crucial properties
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