AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Chemical Composition of Brown Carbon in Tar Ball Aerosols from Biomass Burning
Anusha P.S. Hettiyadura, Chunlin Li, Quanfu He, Yinon Rudich, ALEXANDER LASKIN, Purdue University
Abstract Number: 601 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract Biomass burning (BB) is a major source of brown carbon (BrC) aerosols. BrC causes adverse health effects and alter Earth’s radiative energy balance by absorbing and/or scattering solar radiation or by acting as cloud condensation nuclei. Tar balls, which are submicron sized spherical carbonaceous particles, contribute to a significant fraction of BB BrC. This study explore the chemical composition of BrC in extracted tar ball materials, giving molecular insights to their light absorbing properties. Tar material was generated by heating and dry distilling wood pellets simulating oxidative (in the presence of air) and pyrolysis (in the absence of nitrogen) conditions. The separated aqueous and oil phases were diluted with acetonitrile and analyzed in reversed-phase liquid chromatography coupled with a photodiode array (PDA) detector and a high-resolution OrbitrapTM mass spectrometer (MS). Prior to MS detection the analytes were ionized using either electrospray ionization (ESI) or dopant-assisted atmospheric pressure photo ionization to detect both polar and nonpolar analytes, in both positive and negative ion modes. More than 90% of the organic compounds identified in tar balls were detected in ESI, indicating that most of these compounds contain polar functional groups. A total of 35 common chromophores were detected in all 4 samples. Oil phase samples showed additional chromophores that were retained longer on the column, indicating the presence of nonpolar chromophores in the oil phase compared to the aqueous phase. Furthermore, pyrolysis oil phase displayed more longer-retained chromophores compared to the oxygenated oil phase, reflecting their molecular differences. The light absorbing chromophores identified in this study serve as tracers for BB BrC in the atmosphere and further studies on their light absorbing properties will enable determining their effect on climate forcing.