Secondary organic aerosol (SOA) mass constitutes a significant portion of aqueous aerosol composition, though its mechanisms of formation and exact contributions to overall aerosol properties remains poorly understood. Several products of common aqueous aerosol constituents, such as ammonium sulfate (AS) and methylglyoxal (MG), have been observed to be surface-active, resulting in dramatic changes to overall solution surface tension with relatively small amounts of organic loading. These same solutions are also shown to be sensitive to ultraviolet radiation, in which photobleaching reactions occur that can alter their prevailing compositions and physical properties. While the chromophoric properties of these photobleaching products have been explored, the surfactant properties of these compounds have not been directly measured. Here, small (10µL) droplets of aged MG/AS solutions of varying organic concentration are suspended under dark and irradiated conditions and measured via hanging-drop profile tensiometry. Irradiated droplets were exposed to broadband ultraviolet radiation (λ<sub>max</sub> = 253nm) for durations up to 3 hours. Droplet surface tension was found to depress under irradiated conditions compared to unexposed samples of similar age. UV-visible absorbance spectra were also measured and compared for dark and irradiated droplets under identical conditions. An increase in absorbance in the 280nm region was observed, counter to observed bulk-solution photolysis studies; it is proposed that the sustained high surface-volume ratio of the hanging droplet geometry in the PAT results in partitioning and local concentration effects not observed in previous studies.

<i>In-situ</i> surface tension measurements of hanging droplet methylglyoxal/ammonium-sulfate aerosol mimics under photooxidative conditions

2019 Fall National Meeting

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In-situ surface tension measurements of hanging droplet methylglyoxal/ammonium-sulfate aerosol mimics under photooxidative conditions