Abstract View
Aqueous Phase Photochemical Transformations of Phenolic SOA: Comparisons between OH Radical and Triplet Carbon Oxidation
CHRISTOPHER NIEDEK, Wenqing Jiang, Ryan Farley, Lan Ma, Stephanie Arciva, Cort Anastasio, Qi Zhang, University of California, Davis
Abstract Number: 529
Working Group: Aerosol Chemistry
Abstract
Recent laboratory studies have shown aqueous-phase processing of phenolic compounds, often a large portion of wood combustion emissions, to be a significant source of aqueous SOA (aqSOA). Previous work into phenolic aqSOA relevant to biomass burning emissions has largely focused on relatively unsubstituted phenols (ex. phenol, guaiacol, and syringol). Less attention has been paid to highly substituted phenols which are more likely to partition into the aqueous phase due to their higher Henry’s law constants.
This work is focused on characterizing the aqSOA formed via hydroxyl radical (OH) and triplet excited states of organic compounds (3C*) oxidation of a set of highly substituted phenols (guaiacyl acetone, vanillyl alcohol, syringyl acetone, syringic acid, tyrosol, and ferulic acid) using a soot particle high-resolution aerosol mass spectrometer (SP-AMS). The mass yields, bulk composition, and photochemical evolution of the aqSOA were studied. In addition, a thermodenuder was used upstream of the SP-AMS to gather the volatility profiles of the aqSOA for vanillyl alcohol and 3C*. Some aspects of the bulk composition (ex. elemental ratios like O/C and H/C and signal intensities of C2H3O+ (m/z 43) and CO2+ (m/z 44)) were similar between OH and 3C*-generated SOA. Notably, all aqSOA samples analyzed fall into a relatively small window in H/C-O/C space, implying a high degree of bulk chemical similarity and similar degrees of oxidation between OH and 3C*-generated aqSOA. In contrast, OH-generated SOA had higher levels of acid-functionalization (as evidenced by CHO2+ signal intensity) while 3C*-generated SOA had higher levels of oligomerization (as evidenced by dimer ion signal intensities). Volatility profile analysis demonstrates production of high molecular weight, low-volatility species in the aqSOA of vanillyl alcohol. The mass spectra of each phenolic aqSOA also reveal ions potentially useful as tracer species for ambient studies of biomass burning emissions.