AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Extreme Molecular Complexity Resulting in a Continuum of Carbonaceous Species in Biomass Burning Tar Balls
MATTHEW BREGE, Swarup China, Alla Zelenyuk, Simeon Schum, Lynn Mazzoleni, Michigan Technological University
Abstract Number: 564 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract Wildfire aerosol samples heavily influenced by tar balls were collected in the Pacific Northwest to study the detailed molecular properties and address a critical knowledge gap regarding the chemistry of biomass burning tar balls. The organic aerosol extracts were analyzed using ultrahigh resolution Orbitrap Elite mass spectrometry with four complementary ionization techniques. In addition, the physicochemical properties of individual particles were characterized using micro-spectroscopy and single particle mass spectrometry techniques. The resulting data sets contain upwards of 10,000 distinct molecular formulas observed per sample. Each ionization mode had some fraction of exclusive formulas not detected in the other modes, ranging from 2-24% of the total formulas per sample. A majority of the formulas were CHO or CHNO species and were observed in both samples; in addition, a small number of CH, CHN and CHOS formulas were also observed. The overall average O/C ratios were approximately 0.36 with a range of 0-2.3. Many of the molecular formulas appear to be derivatives of polycyclic aromatic hydrocarbons and nitro-phenolic compounds with saturation mass concentrations defined as low or extremely low volatile organic compounds. The estimated dry glass transition temperatures implied that a majority of formulas would be a solid or semi-solid at their respective ambient temperatures. The estimated dry glass transition temperatures increased with molecular weight and the estimated volatilities decreased with molecular weight, consistent with literature expectations. In both of these samples, we observe a continuum of carbonaceous species, which are comprehensive in the observed ranges of oxidation and hydrogen saturation. The observed species span nearly the entire theoretical space of possible molecular formulas for the molecular weight ranges analyzed. This continuum has strong implications for the characterization of organic aerosol, where we expect an exhaustive agglomeration of chemical species to be present at low concentration.