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Molecular-Specific Optical Properties of Atmospheric Brown Carbon Proxies
ANUSHA P.S. HETTIYADURA, Valeria Garcia, Christopher West, Jay Tomlin, Chunlin Li, Quanfu He, Yinon Rudich, Alexander Laskin, Purdue University
Abstract Number: 271
Working Group: Carbonaceous Aerosol
Abstract
This study explores the chemical composition and light absorption properties of biomass tar condensates as proxies of atmospheric brown carbon (BrC) emitted from biomass burning (BB). The condensates were generated from dry-distilling wood pellets simulating oxidative and pyrolysis BB conditions. Both condensates separated into two immiscible, ‘darker oily’ and ‘lighter aqueous’, phases. These phases were separately analyzed using reversed-phase high performance liquid chromatography (HPLC) coupled with a photodiode array (PDA) detector and a high-resolution mass spectrometer (HRMS) interfaced with interchangeable electrospray and atmospheric pressure photo ionization sources. Based on HPLC-PDA-HRMS results, two sets of BrC chromophores were identified: 1) less absorbing, polar mono-aromatic species, common among different fractions, and 2) more absorbing, non-polar poly-aromatic species, specific to oily fractions. Chemical composition of BrC chromophores is inferred from the correlative analysis of the HRMS and PDA records: furans and 2-methoxyphenols are identified as the major common chromophores and oxidized diterpenoids and alkyl phenanthrenes are identified as the major oil-specific chromophores. The pyrolysis oily (PO) phase showed the highest UV-Vis absorption and was used to generate BrC aerosol, followed by 1) collection of the size-separated aerosol samples using a cascade impactor, and 2) their analysis using the HPLC-PDA-HRMS platform. Aerosolized PO samples showed substantial increase in their corresponding mass absorption coefficient (MAC300-428 nm) compared to that of the bulk PO sample. We show that the increase of MAC values caused by evaporation and gas-phase partitioning of relatively volatile, low-MW and less-absorbing chromophores. The optical properties of the aerosolized PO were consistent with the reported measurements of ambient BB-BrC aerosol.