AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
The Influence Pre-existing Organics on Secondary Organic Aerosol Formation from Reactive Uptake of Isoprene Epoxydiols in a Regional Scale Model
MUTIAN MA, Havala Pye, Yue Zhang, Yuzhi Chen, Chitsan Wang, Jason Surratt, William Vizuete, University of North Carolina at Chapel Hill
Abstract Number: 107 Working Group: Regional and Global Air Quality and Climate Modeling
Abstract Isoprene oxidation products formed under low-nitric oxide (NO) conditions are important precursors for the formation of particulate matter (PM). Specifically, isoprene epoxydiols (IEPOX), an abundant isoprene-derived oxidation product, forms secondary organic aerosol (SOA) via acid-catalyzed multiphase (heterogeneous) reactions. Recent experimental studies at UNC-Chapel Hill, using synthetically-derived IEPOX, have quantified the reactive uptake of IEPOX to determine how much gas-phase IEPOX could form SOA. An accurate description of this process is critical in regulatory modeling to predict the formation of SOA. These experiments, however, consisted only of pure sulfate aerosol of varying acidity without a pre-existing organic coating. Under some atmospheric conditions, organic layers can exist on pre-existing aerosols potentially changing both the physical and chemical properties of IEPOX-derived SOA. Prior experiments, using -pinene as a surrogate for an organic coating on an ammonium bisulfate seed, have found that IEPOX uptake ceased when the mass of alpha-pinene derived coating exceeds 85% of the total aerosol mass. Ongoing experiments at UNC are quantifying how the thickness and type of organic coating at varying levels of relative humidity will influence IEPOX diffusivity within the aerosol phase. Leveraging this new data, we will estimate the impact of organic coating on regional model predictions of IEPOX-derived SOA using the Community Multiscale Air Quality (CMAQ) v5.2 system. This version of CMAQ was developed by Environmental Protection Agency (EPA) and includes IEPOX and aqueous-phase chemical reaction pathways leading to IEPOX-derived SOA formation. These modeling algorithms, however, have yet to include the influence of pre-existing organic coatings. Using the new UNC experimental data as a guide, we will provide sensitivity runs changing the reactive uptake parameter and predicting the change in IEPOX-derived SOA. This modeling episode also coincided with the Southern Oxidant and Aerosol Study (SOAS), allowing for comparisons with measured IEPOX-derived SOA.