Organic compounds, specifically secondary organics, are known to play an essential role in determining the structure and characteristics of aqueous aerosols and therefore have significant impacts on the overall climate. However, the formation and end fate of these organics are poorly understood. Furthermore, atmospheric aerosols are also known to have high salt concentrations, which can have synergistic interactions with organics, further complicating these systems. Elucidating the chemistry of aerosol interfaces is essential in understanding aerosol behavior in the environment. Methylglyoxal (MG) is an abundant atmospheric α-dicarbonyl found in secondary organic aerosols (SOAs), which is known to readily hydrate to form both a diol and tetrol. MG is currently an organic of significant interest because the amount of SOA containing MG and the concentration of MG within said SOA are higher than predicted by standard SOA formation mechanisms. We have previously studied methylglyoxal at the neat air-water interface and found that the MG diol to tetrol ratio is greater at the interface than in bulk, favoring the diol. Here we investigate the effect of a non-reactive inorganic salt, NaCl, on methylglyoxal at the planar air-water interface as a model for aqueous aerosols. This system was experimentally observed using vibrational sum-frequency spectroscopy (VSFS) and surface tensiometry. Calculated VSFS spectra were generated using classical dynamics and quantum mechanical methods and compared to experimental results. Our results indicate that the NaCl causes a shift in the hydration equilibrium between the MG diol and tetrol to further favor the diol at the interface. This work provides the foundation for future studies of more complicated atmospherically relevant systems.

Effects of sodium chloride on the behavior of methylglyoxal at the air-water interface

253rd National Meeting (2017)

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