Probing Reaction Pathways of Organic Radicals in the Atmospheric Aqueous Phase
LEXY LEMAR, Victoria Barber, Seamus Frey, Yaowei Li, Frank Keutsch, Jesse Kroll, MIT
Abstract Number: 116
Working Group: Aerosol Chemistry
Abstract
The oxidation reactions that lead to the formation of secondary organic aerosol (SOA) can occur in both the gas phase and the condensed phase. Critical to these processes are the chemistry of key organic radical intermediates (R, RO, and RO2); while the reactions of these species in the gas phase have seen substantial study, their reactions in the atmospheric aqueous phase (i.e., cloud droplets, deliquesced aerosol particles) have not. The presence of liquid water could affect this chemistry, and ultimately product distributions, due to locally high concentrations, solvent effects, and competition with reactions unique to the aqueous phase, such as oligomerization or hydrolysis. In this study, we investigate how the reaction pathways of alkoxy (RO) and peroxy (RO2) radicals differ between the gas and aqueous phases through the use of an environmental chamber and bulk aqueous reactor. A suite of real-time analytical instruments (an aerosol mass spectrometer, a chemical ionization mass spectrometer, and a scanning mobility particle sizer) is used to measure both gas- and aerosol-phase products, yielding insight into reaction mechanisms and branching ratios. Direct comparison of the evolution of various products across phases provides new insight into how phase affects radical reactivity, enabling the improved understanding of SOA and other species formed from aqueous-phase oxidation.