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Secondary Organic Aerosol Formation from Reaction of 3‑Methylfuran with Nitrate Radicals

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journal contribution
posted on 23.04.2019 by Taekyu Joo, Jean C. Rivera-Rios, Masayuki Takeuchi, Matthew J. Alvarado, Nga Lee Ng
A significant amount of furan species is emitted from biomass burning. They are highly reactive to hydroxyl (OH) and nitrate radicals (NO3), which can lead to the formation of secondary organic aerosol (SOA). Here, we investigate gas-phase oxidation and SOA formation from 3-methylfuran (C5H6O) via NO3 reaction. Experiments are performed under dry conditions (RH < 5%) and with different initial concentrations of 3-methylfuran (from 95.9 to 562.8 ppb). We demonstrate that this reaction leads to SOA formation, with SOA yield ranging from 1.6 to 2.4% for organic mass loading ranging from 5.1 to 45 μg/m3. More than half of the SOA mass is generated after complete depletion of 3-methylfuran, highlighting the importance of higher-generation or multiphase reactions to aerosol formation. Particle-phase organic nitrates contribute 39.4% of organics and their average volatility (average C* = 10–2.9 μg/m3) is higher than that of non-nitrate organic compounds (average C* = 10–3.3 μg/m3). A reaction mechanism is proposed based on the identified products, and C5H5NO5 and C5H6O3 are determined to be the major species in the gas and particle phases, respectively. Oligomer formation appears to determine the SOA composition and formation rate, and both gas-phase ROOR′ formation via RO2 + RO2 (acylperoxy radical) reactions and particle-phase accretion reactions can lead to the formation of the dimeric (C10) compounds observed. Results from this study provide detailed chemistry of 3-methylfuran oxidation that can improve our understanding of its impact on SOA and ozone formation in nighttime biomass burning plumes.