Citation:

chen, y., A. Ng, J. Green, Y. Zhang, M. Riva, T. Riedel, H. Pye, Z. Lei, N. Olson, M. Cooke, Z. Zhang, W. Vizuete, A. Gold, B. Turpin, A. Ault, AND J. Jason D. Surratt. Applying a Phase-Separation Parameterization in Modeling Secondary Organic Aerosol Formation from Acid-Driven Reactive Uptake of Isoprene Epoxydiols under Humid Conditions. ACS ES&T Air. American Chemical Society, Washington, DC, , N/A, (2024). https://doi.org/10.1021/acsestair.4c00002

Impact/Purpose:

Isoprene is the most abundant non-methane organic compound emitted to the atmosphere. In the atmosphere, isoprene reacts to form products that can dissolve in liquid phases and further react to form fine particle mass (PM2.5). This work examines how the composition and morphology of particles affects the conversion of isoprene products to PM2.5. This work will inform CRACMM version 3 in the Community Multiscale Air Quality (CMAQ) modeling system. CMAQ is used to predict ambient air endpoints for various efforts and data products.

Description:

Secondary organic aerosol (SOA) from acid-driven reactive uptake of isoprene epoxydiols (IEPOX) contributes up to 40% of organic aerosol (OA) mass in fine particulate matter. Previous work showed substantial conversions of particulate inorganic sulfates to surface-active organosulfates (OSs) by IEPOX decreases aerosol acidity and creates a viscous organic-rich shell that poses as a diffusion barrier, inhibiting additional reactive uptake of IEPOX. To account for this “self-limiting” effect, a phase-separation box model was developed to evaluate parameterizations of IEPOX reactive uptake against time-resolved chamber measurements of IEPOX-SOA tracers, including 2-methyltetrols (2-MT) and methyltetrol sulfates (MTS), at ~ 50% relative humidity. The phase-separation model was most sensitive to the mass accommodation coefficient, IEPOX diffusivity in the organic shell, and ratio of the third-order reaction rate constants forming 2-MT and MTS (kMT/MTS). In particular, kMT/MTS had to be lower than 0.1 to bring model predictions of 2-MT and MTS in closer agreement with chamber measurements, while prior studies reported values larger than 0.71. The model-derived rate constants favor more particulate MTS formation due to 2-MT likely off-gassing at ambient-relevant OA loadings. Incorporating this parametrization into chemical transport models is expected to predict lower IEPOX-SOA mass and volatility due to the predominance of OSs.

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