AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Application of a Reactive Uptake Parameterization Considering Non-Ideal Effects and Phase State in Simulating Secondary Organic Aerosols from Isoprene Expoxydiols Under Controlled Laboratory Measurements
YUZHI CHEN, Yue Zhang, Matthieu Riva, Theran P. Riedel, Havala Pye, Nicole Olson, Ziying Lei, Zhenfa Zhang, Avram Gold, Barbara Turpin, Andrew Ault, Jason Surratt, University of North Carolina at Chapel Hill
Abstract Number: 391 Working Group: Aerosol Chemistry
Abstract Isoprene epoxydiols (IEPOX), OH-initiated oxidation products of isoprene, are known to produce secondary organic aerosol (SOA) in the presence of acidic sulfate-containing aerosols within the atmosphere. IEPOX-derived SOA can contribute up to 40% of OA mass in isoprene-rich regions such as the southeastern U.S. Representing efficiency of uptake by a coefficient (γIEPOX) has been convenient for predicting IEPOX-SOA in chemical transport models. However, large uncertainties are associated with such approach. A laboratory study has shown that the available condensed-phase reaction-rate constants are likely under-predicted as they fail to predict the extensive conversion of inorganic sulfate to organic sulfate by IEPOX. The substantial formation of surface-active organosulfates results in a particulate morphology with a viscous organic-rich shell surrounding an aqueous inorganic core. Consequently, acid-driven reactive uptake of IEPOX is inhibited by the growing organic shell over time. This so-called “self-limiting” effect, along with the potential under-prediction of kinetic parameters has yet to be investigated in a controlled environment.
In this work, time-resolved condensed-phase concentrations of IEPOX-SOA molecular tracers were obtained from chamber experiments conducted with authentic trans-β-IEPOX and acidic sulfate aerosols. A one-dimensional box model considering the “self-limiting” effect was used to derive and evaluate reactive uptake parameterization against measurements. Newly derived condensed-phase reaction-rate constants forming major SOA tracers were found to be at least 2 orders of magnitude higher than those used in the current models, consistent with those derived from computational chemistry. Sensitivity analyses were performed, and recommended values were given for other relevant parameters, including Henry’s law constants and IEPOX diffusion coefficient in the organic shell of IEPOX-SOA. Current air quality and global models need to be updated to assess the improved parameterization derived from this work, which is critical to understanding the processes that govern formation of IEPOX-SOA in the atmosphere and developing air-pollution mitigation strategies.