The release, natural or anthropogenic, of volatile organic compounds (VOCs) results in a series of oxidation reactions that lead to the formation of secondary organic aerosols (SOAs). SOAs contribute to increased PM2.5, an EPA-regulated air pollutant, and poorer air quality. Many SOA precursors and their oxidation products are water-soluble, and thus, could be taken up in liquid water present in the atmosphere. Salt identities and concentrations in aerosol liquid water (ALW) vary and can modulate organic partitioning behavior. Current research has not quantified the effects of salt concentration on the partitioning of water-soluble components and precursors of SOA. Using a combination of an oxidation flow reactor and an impinger to collect water-soluble organic vapors from isoprene oxidation, salting effects were studied for this photooxidation system with NaCl at varying ionic strengths and pH. Water soluble organic gases (WSOCg) were quantified in each sample using UV/Vis spectroscopy. Initial UV/Vis data suggest that NaCl concentrations above 1 molal exhibit salting out effects of WSOCg. Further, preliminary results from high resolution mass spectrometry (HPLC-PDA-HRMS) showed that there appear to be hydration reactions between WSOCg and the experimental solutions. These reactions may increase the amount of WSOCg able to dissolve compared to theoretical calculations, which use thermodynamic calculations based on Henry’s constants of the WSOCg. This work provides a framework for studying modulation of organic partitioning as a function of inorganic salt concentrations and identities, such as ammonium sulfate.

Uptake of trace gases produced by photooxidation of isoprene into atmospheric aqueous droplets

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