Evaluation of Regional-Scale Model Parameters in the Prediction of Isoprene Epoxydiol (IEPOX)-Derived Secondary Organic Aerosols (SOA) Generated during Laboratory Chamber Experiments

ALEXANDRA NG, Yuzhi Chen, Jaime Green, Jason Surratt, Haofei Zhang, William Vizuete, University of North Carolina at Chapel Hill

     Abstract Number: 395
     Working Group: Aerosol Chemistry

Abstract
Isoprene epoxydiol (IEPOX)-derived secondary organic aerosols (SOA) are formed in humid, low nitric oxide (NO) environments from the acid-controlled reactive uptake of gas-phase IEPOX to pre-existing sulfate aerosols. IEPOX SOA have been found to contribute up to 30% of organic aerosols in the Southeastern United States and Amazon rainforest. IEPOX SOA tracers consist primarily of 2-methyltetrols (2-MT) and 2-methyltetrol sulfates (2-MTS), which can subsequently form dimers and higher order oligomers. IEPOX SOA tracers can phase separate to form a viscous organic shell with an inorganic core. This core-shell morphology can inhibit reactive uptake of IEPOX and affects the acidity and kinetics of IEPOX SOA formation. Due to the importance of this SOA pathway, IEPOX SOA chemistry has been implemented in regional scale models with varying complexity, such as in the Community Multiscale Air Quality (CMAQ) Modeling System and Weather Research, and Forecasting model coupled with Chemistry (WRF-Chem). In this work, important parameters (reaction rate constants, Henry’s law coefficient, thermodynamically modeled acidity) used by these modeling systems to predict IEPOX SOA formation and IEPOX reactive uptake were investigated in a box model to identify sensitivities to kinetics, diffusivity, and acidity changes. This evaluation included indoor chamber experiments conducted by collaborator, Yuzhi Chen, with environmental sensitivities to the IEPOX:Sulfate ratio at a fixed initial aerosol pH (i.e., 1.5). Base model parameter results were compared to an optimized model that could predict experimental measurements. CMAQ and WRF-Chem approaches were modified to include the latest state-of-the-science on IEPOX SOA formation kinetics, phase state parameters, and the inclusion of organic acidity. This work provides insights into the physiochemical properties and modeling parameters critical to formation of IEPOX SOA with chamber-based measurements.

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