Trace amounts of water-soluble Fe(III) are commonly present in atmospheric aerosols and cloud water in areas affected by wind-blown mineral dust. When later interact with organic carboxylic acids from anthropogenic pollution, the resulting airborne mixtures often contain photo-catalytically active Fe-organic complexes that trigger a range of chemical reactions in these complex systems. Chemical composition and atmospheric transformations of these mixtures are uncertain, making it challenging to estimate their resulting impact on atmospheric environment, climate forcing, and air quality. This work presents a systematic investigation of the molecular-level composition and the extent of aqueous photochemical processing of Fe-organic complexes in laboratory mimics of atmospheric aerosols and cloud water. In our ongoing work, selected Fe-organic compounds are photolyzed under 365 nm light, followed by in-depth chemical analysis of mixtures withdrawn at different times of the experiment. Here, we present a set of experiments where photochemical transformations of Fe-citrate system was studied in detail. We used UV-Visible spectroscopy to monitor overall extent of the reaction and determine its effects on the light absorption by the bulk sample. We also performed separation of chemical species in these mixtures using high-performance liquid chromatography coupled to photo diode array and high-resolution mass spectrometry detection. We show composition changes in the Fe-citrate system before and after photolysis revealing new light absorbing products are formed upon photolysis. The results suggest that Fe-complexes are important reaction intermediates with vital impact on the atmospheric aging of organic aerosol, its light-absorbing properties and propensity to generate particle-phase reactive oxygen species.

Probing molecular composition of Iron-organic complexes and their photochemical products in laboratory mimics of atmospheric aerosol and cloud water

2019 Spring National Meeting

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