A unique application of single particle scanning transmission X-ray microscopy (STXM) and atomic force microscopy (AFM) is presented for quantitative analysis of density, water uptake and chemical transformations of individual submicrometer particles. The approach utilizes the exposure of substrate-deposited individual particles to water vapor at different relative humidity followed by STXM/AFM spectromicroscopy analysis. The hygroscopic properties of several atmospherically relevant inorganic salts and carboxylic acids have been quantified in terms of the total mass of water and corresponding water-to-solute ratio. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to monitor chemical changes within an individual particle at different relative humidity (RH). STXM/NEXAFS measurements acquired at different RH show efficient keto-enol tautomerization of carboxylic acids, with the enol form dominating at higher RH. Our results suggest that in deliquesced submicrometer-sized particles, carboxylic acids may exist in predominantly enol forms that need to be explicitly considered in atmospheric aerosol chemistry.

Spectromicroscopy study of chemical transformation and water uptake on individual submicrometer particles

243rd National Meeting (2012)

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