EC-20. Henry's Law Partitioning and Setschenow Salting Constants of 1,2-ISOPOOH in Aqueous Solutions Containing Ammonium Sulfate and Sodium Oxalate

Isoprene is the predominant biogenic emission from plants and contributes approximately 30% of global non-methane volatile organic carbon (VOC) emissions. Isoprene hydroxyhydroperoxides (ISOPOOHs) are a first-generation of isoprene oxidation in low-NOx conditions. The further oxidation of ISOPOOHs can affect aerosol growth through the production of secondary organic aerosol (SOA) precursors (Rivera Rios 2018). The equilibrium between ISOPOOH in the gas and particle phases is governed by Henry’s Law. The Henry’s Law constant changes as a function of salt concentration in the aerosol phase according to the relation: ln⁡(H_s/H_0)= k_s m, where H_s and H_0 are the Henry’s Law constants in the salt solution and pure water, respectively, k_s is the Setschenow coefficient, and m is the molality (Ruckenstein, E., Shulgin, I 2002). Iodine chemical ionization mass spectrometry (I- CIMS) was used to measure the Setschenow constant for 1,2-ISOPOOH with ammonium sulfate and sodium oxalate, common salts found in aerosols. Aqueous mixtures with known concentrations of 1,2-ISOPOOH and salt were placed in a flask. A humidified N2 gas flow was brought over the sample as it came to an equilibrium. The ISOPOOH gas phase signal was measured by a Tofwerk L-ToF mass spectrometer coupled with a VOCUS AIM ion source. The aqueous phase concentration was measured by a derivatization/colorimetric spectrophotometric method (Ranney, A.P., Ziemann, P.J 2016). The Setschenow constants were determined to be 0.18722 +/- 0.00451 L/mol and 3.6039 +/- 0.158 L/mol for ammonium sulfate and sodium oxalate, respectively. The Henry’s Law constant was determined to be between 2.5E+05 M/atm and 7.0E+05 M/atm. This is greater than values reported in literature. Rivera Rios reports 1.18E+05 M, atm, the EVAPORATION+AIOMFAC model reports 1E+05 M/atm, and the GROMHE model reports 1.3E+05 M/atm (Rivera Rios 2018). References: (1) Rivera Rios, J.C.: Atmospheric Chemistry of Isoprene Hydroxyhydroperoxides (2018) (2) Ruckenstein, E., Shulgin, I.: Salting-Out or –In by Fluctuation Theory. Ind. Eng. Chem. Res. 41, 4674-4680 (2002) (3) Ranney, A.P., Ziemann, P.J.:: Microscale Spectrophotometric methods for Quantification of Functional Groups in Oxidized Organic Aerosol. Aerosol Science and Technology. 9, 881-892 (2016)