Illuminating Chemical Mechanism Gaps through Modeling Secondary Pollutants from Volatile Chemical Products
AMEL KSAIBATI, Huiying Luo, Abraham Dearden, Matthew Coggon, Katelyn Rediger, Carsten Warneke, Lu Tan, Damien Ketcherside, Lu Hu, Cort Zang, Tucker Melles, Audrey Lawrence, Megan Willis, Lauren A. Garofalo, Delphine K. Farmer, Shantanu Jathar, Colorado State University
Abstract Number: 289
Working Group: Aerosol Chemistry
Abstract
Chemical mechanisms used in atmospheric studies describe the complex gas- and particle-phase chemistry of volatile chemical product (VCP) VOCs, yet gaps in representation or reliance on surrogate species often hinder accurate predictions of secondary pollutants such as ozone (O3) and secondary organic aerosol (SOA). As VCP-derived VOC emissions dominate most urban VOC sources, addressing these deficiencies is critical for advancing air quality modeling. This study addresses the gap by using the Framework for 0-D Atmospheric Modeling and its aerosol module extension (F0AM-WAM) to simulate coupled gas-phase and organic aerosol formation and compare predictions with experimental observations. Recently, environmental chamber experiments performed at Colorado State University investigated the oxidation chemistry of 14 diverse VCP OVOC species, including benzyl alcohol, carbitol, and furan. Assessed mechanisms include the Master Chemical Mechanism (MCM) for well-characterized VOCs and the GECKO-A mechanism generator for structurally complex or underrepresented species. Model outputs were compared against gas-phase measurements (e.g., O3, NO, NO₂), SOA yield, and high-resolution mass spectrometer data (e.g., PTR-ToF-MS, NH₄⁺-CIMS). Carbitol for example, a solvent commonly added to inks and wood stains, is not explicitly accounted for in MCM and a smaller glycol ether is used as a surrogate in its place. When surrogate species in MCM deviate from experimental observations, and corresponding explicit species in GECKO-A yield better performance, it underscores the need to extract and develop reduced forms of these well-performing species and replace underperforming surrogates. While model predictions capture observed trends for certain OVOCs, substantial discrepancies persist for oxygenated intermediates and secondary products. This highlights limitations in current representations of VCP OVOC chemistry. Insights from this work will inform recommendations to improve VCP OVOC chemistry in atmospheric chemical mechanisms, ultimately enhancing 3-D atmospheric model predictions of air quality and human exposure risks.