AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Brown Carbon Formation from Nighttime Chemistry of Unsaturated Heterocyclic Volatile Organic Compounds
Huanhuan Jiang, Alexander Frie, Avi Lavi, Jin Chen, Haofei Zhang, Roya Bahreini, YING-HSUAN LIN, University of California, Riverside
Abstract Number: 743 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract Nighttime atmospheric processing enhances the formation of brown carbon aerosol (BrC) in biomass burning plumes. Heterocyclic compounds, a group of volatile organic compounds (VOCs) abundant in biomass burning smoke, are possible BrC sources. We investigated the nitrate radical (NO3)-initiated oxidation of three model heterocyclic VOCs, including pyrrole, furan, and thiophene, as a source of BrC. Utilizing complementary online and offline techniques, we determined the imaginary component of the refractive index at 375 nm (k375), the single scattering albedo at 375 nm (SSA375), and mass absorption coefficients (MAC, 290–700 nm) of the resulting secondary organic aerosol (SOA). Compared to furan and thiophene, NO3 oxidation of pyrrole has the highest SOA yield. Pyrrole SOA is also more absorbing than furan SOA and thiophene SOA. Compared to other SOA systems, MACs reported in this study are higher than those from biogenic precursors and similar to high-NOx anthropogenic SOA. High-resolution mass spectrometric measurements revealed unsaturated heterocyclic nitro compounds or organonitrates as possible chromophores in BrC from all three precursors. These findings imply that nighttime oxidation of fire-sourced heterocyclic VOCs, particularly pyrrole, is a plausible source of BrC.