Effects of Humidity on Secondary Organic Aerosol Formation from Furanoid Oxidation with Hydroxyl Radicals

TAEKYU JOO, Jean Rivera-Rios, Tori Hass-Mitchell, Jo Machesky, Drew Gentner, Matthew Alvarado, Nga Lee Ng, Georgia Institute of Technology

     Abstract Number: 294
     Working Group: Aerosol Chemistry

Abstract
Biomass burning emits substantial amounts of non-methane organic compounds (NMOCs) that can contribute to the formation of secondary organic aerosol (SOA). Recent studies suggest that a large fraction of SOA can be produced from non-traditional precursors, including furanoids, that are highly reactive with common atmospheric oxidants. Here, we investigate SOA formation from photooxidation of furfural, 2-methylfuran, and 3-methylfuran in the Georgia Tech Environmental Chamber (GTEC) facility. Experiments are performed under dry (RH<5%) and humidified (RH 50 – 60%) conditions with ammonium sulfate seed aerosols in the presence of NO_x. For all precursors, SOA yields are found to be higher under humid conditions. Across the three precursors, SOA yields and the resulting organic aerosol loadings (ΔM_o) from furfural were 6 – 10 times and 5 – 9 times higher, respectively, than that from 2-methylfuran and 3-methylfuran. For furfural, rapid SOA formation was observed under humid condition, whereas under dry conditions SOA was formed slowly and steadily until the end of the experiments. Both 2-methylfuran and 3-methylfuran experiments also show non-negligible SOA formation after the depletion of precursors under both RH conditions. We propose reaction mechanisms based on the compounds identified using a Filter Inlet for Gases and AEROsols coupled with a time-of-flight chemical ionization mass spectrometer (FIGAERO-HR-ToF-CIMS). The temporal evolution and thermograms of particle-phase species point to differences in oxidation and oligomerization mechanisms under different precursor and RH conditions. We find that fast uptake of furfural and first-generation products contribute to the rapid SOA formation rate under humid conditions in furfural experiments, and different peroxy radical branching pathways drive its higher SOA formation potential compared to methylfurans. These results contribute to our understanding of the oxidation of furans under different meteorological conditions and SOA formation in biomass burning plumes.