AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Combined Impacts of Acidity and Viscosity on the Formation of Inorganic-Organic Mixed Isoprene Epoxydiol (IEPOX)-Derived Aerosols
YUE ZHANG, Yuzhi Chen, Ziying Lei, Nicole Olson, Matthieu Riva, Abigail Koss, Zhenfa Zhang, Avram Gold, John Jayne, Douglas Worsnop, Timothy Onasch, Barbara Turpin, Jesse Kroll, Andrew Ault, Jason Surratt, University of North Carolina at Chapel Hill
Abstract Number: 734 Working Group: Aerosol Chemistry
Abstract Acid-driven reactions are an important formation mechanism for atmospheric secondary organic aerosol (SOA). Isoprene-derived SOA is often formed through acid-driven reactive uptake of isoprene-derived epoxydiols (IEPOX) onto acidic sulfate particles. These multiphase processes convert a significant portion of the inorganic sulfate into organosulfates, during which changes in aerosol physicochemical properties have not been well characterized. This study systematically examines the phase state, acidity, and morphology of aerosol particles as IEPOX reacts with acidified ammonium sulfate particles.
Chamber studies show that heterogeneous reactions of IEPOX is accompanied by the rapid formation of IEPOX-derived SOA, but further IEPOX uptake is impeded by its reaction products, especially the organosulfates. To explain such phenomenon, a thermodynamic model and a viscosity model are combined to predict the drastic changes of aerosol viscosity and acidity during this process. Notably, the hydronium ion (H+) aerosol concentration decreases nearly by 1.5 pH units, and viscosity increases by more than 7 orders of magnitude from the beginning of the reaction to the end. SOA converts into a core-shell morphology with inorganic components remaining in the core and the organic components in the shell. Initial IEPOX-to-inorganic sulfate ratios as well as aerosol acidity and viscosity play critical roles in the inhibition of additional multiphase chemical reactions of IEPOX, explaining the self-limiting effect of IEPOX-derived SOA formation. Drastic changes in aerosol acidity and viscosity result in significant changes in the physicochemical properties of aerosols, which in turn alters the chemical reactivity. Our findings reveal important interconnections between the physical and chemical properties of the aerosol particles that come from interactions of inorganic and organic components. These results have important implications for understanding isoprene-derived SOA formation and the interplay between multiphase chemical processes that ultimately control atmospheric SOA formation and its impact on climate, human health, and visibility.