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Effects of Different Environmental Conditions on Secondary Brown Carbon Formation from Nighttime Oxidation of Furan
KUNPENG CHEN, Nilofar Raeofy, Raphael Mayorga, Roya Bahreini, Haofei Zhang, Ying-Hsuan Lin, University of California, Riverside
Abstract Number: 557
Working Group: Aerosol Chemistry
Abstract
Brown carbon (BrC) contributes to a large uncertainty of direct radiation effects of aerosols in the troposphere. Particularly, nighttime oxidation of heterocyclic volatile organic compounds (VOCs) (e.g., furan) may be a potentially important source of secondary BrC aerosols, but the chemical compositions and optical properties are not fully constrained. Here we performed chamber experiments to simulate nighttime oxidation of furan by nitrate radicals (NO3), which was generated from the reaction between nitrogen dioxide (NO2) and ozone (O3). In our study, we explored the effects of different environmental conditions, including low/high concentration ratio of NO2 and O3 (i.e. [NO2]/[O3] = 0.1 or 0.3), the presence of seed particles (ammonium sulfate) and low/high relative humidity (RH < 10% and 50-70%) on BrC formation. Our results showed that under low RH, both high [NO2]/[O3] and the presence of seeds could increase the SOA yield, but different value of [NO2]/[O3] did not affect the size distribution of particles. To explore the light absorption of BrC constituents, we performed ultraviolet-visible (UV-Vis) measurements at 290-700 nm for the aerosol samples extracted by acetonitrile. The calculated mass-normalized absorption coefficient (MAC) indicated that both high [NO2]/[O3] and the presence of seeds could increase the average MAC under low RH. However, analysis of functional groups by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) suggested that BrC constituents corresponding to high and low [NO2]/[O3] are similar in the presence of seeds, but different in the absence of seeds. The results of high RH experiments, and a comprehensive analysis of molecular compositions and candidates of chromophores by online and offline characterizations (i.e., iodide-adduct FIGAERO-HR-TOFCIMS and UPLC-DAD-ESI-QTOFMS) will be discussed as well. This study demonstrated that environmental conditions may significantly alter the optical properties and chemical compositions of secondary BrC aerosols.