Oxidative History Controls the Composition and Fate of Biomass-Burning-derived Phenolic compounds: Sequential OH and NO3 Oxidation
MADELEINE SZE IN NG, David Pando, Bin Bai, Heather O. LeClerc, Pengfei Liu, Drew Gentner, Andrew Lambe, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 555
Working Group: Aerosol Chemistry
Abstract
Biomass burning (BB) is a major source of phenolic volatile organic compounds (VOCs), contributing significantly to secondary organic aerosol (SOA) and brown carbon (BrC) through atmospheric oxidation. While nighttime nitrate (NO3) radical oxidation of these VOCs forms BrC, real-world BB plumes experience sequential oxidation cycles, during which the NO3 reactivity of phenolic VOCs and their early-generation products are potentially influenced by daytime exposure to hydroxyl (OH) radicals.
To simulate diel atmospheric oxidation of phenolic VOCs, we present results from serial OH-NO3 oxidative aging experiments combining the Georgia Tech Environmental Chamber (GTEC) and a Potential Aerosol Mass oxidation flow reactor (OFR). We focus on three representative phenolic VOCs – phenol (C6H5(OH)), guaiacol (monomethoxy phenol; C6H5(OH)(OCH3)), and syringol (dimethoxy phenol; C6H5(OH)(OCH3)2). Together, they represent the chemical diversity and atmospheric reactivity of phenolic VOCs, allowing us to elucidate how varying functional groups modulate sequential oxidation processes and SOA evolution. Time-resolved gas and aerosol chemical composition is monitored using an Aerosol Mass Spectrometer (AMS) and the Filter Inlet for Gases and Aerosol-Iodide-Chemical Ionization Mass Spectrometer (FIGAERO-I–-CIMS), which measure gas- and particle-phase products as a function of OH and NO3 exposure, with additional chemical speciation via offline samples. The results demonstrate how progressive daytime oxidation fragments and functionalizes phenolic precursors and their early-generation oxidation products. Our preliminary result suggests that in general, NO3 reactivity toward the plume is dependent on its daytime gas-phase OH aging, in which more-oxidized products produced in daytime may experience less subsequent NO3-driven chemical changes. This OH oxidation-induced suppression potentially alters the chemical composition, SOA formation, and optical properties of BB SOA during nighttime. Our findings highlight the important role of diurnal oxidation cycling in controlling BB plume evolution, offering experimental constraints for improving the treatment of smoke plumes in atmospheric and climate models.