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Molecular Investigation of the Multi-Phase Photochemistry of Fe-citrate Aerosol Proxies
CHRISTOPHER WEST, Jackson Ryan, Felipe Rivera-Adorno, Ana Morales, Jay Tomlin, Anusha P.S. Hettiyadura, Maria Misovich, Andrew Darmody, Peng Lin, Brittany Linn, Alexander Laskin, Purdue University
Abstract Number: 215
Working Group: Aerosol Chemistry
Abstract
Soluble Fe(III) on Earth is ubiquitously present in terrestrial, oceanic, and surface waters, mineral-rich soil, vegetative crops, plants, and atmospheric particulate matter. Upon dissolution of Fe3+ from wind-blown dust or atmospheric cloud water, organic carboxylic acids efficiently chelate dissolved Fe3+ to form photo-catalytically active Fe(III)-carboxylate complexes that catalyze a range of radical-induced chemical reactions in these complex aerosol/aquatic systems. The chemical composition and atmospheric transformations of these mixtures are ambiguous, making it challenging to estimate their resulting impact on the aqueous-phase chemistry of atmospheric aerosols. This work presents a systematic investigation of the molecular composition and the extent of aqueous photochemical processing of Fe(III)-citrate complexes as laboratory proxies of atmospheric water. We monitored the overall extent of the reaction and determine its effects on the light absorption by the bulk material. Water-soluble chemical constituents from each of the photoreacted mixtures were separated and characterized using liquid chromatography, photodiode array, and electrospray ionization high-resolution mass spectrometry platform. In addition, colloidal material formed in the photoreacted samples was aerosolized and probed by the soft X-ray spectro-microscopy. The aqueous-suspended colloidal material was also probed using dynamic light scattering methods. We demonstrate for the first time a high-level optical and molecular description of the water-soluble components (i.e. FeIII/II-organic complexes, oligomers, and organic acid products) along with chemical imaging of ‘pyrolytic-like’ solid carbonaceous colloids formed during the photolysis reactions.