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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
05 Jul 2017
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.
Bulk and Molecular-Level Characterization of Laboratory-Aged Biomass Burning Organic Aerosol from Oak Leaf and Heartwood Fuels
Claire F. Fortenberry1, Michael J. Walker1, Yaping Zhang1, Dhruv Mitroo1,a, William H. Brune2, and Brent J. Williams1 1Department of Energy, Environmental, and Chemical Engineering, Washington University in Saint Louis, Saint Louis, MO 63130, USA
2Department of Meteorology and Atmospheric Science, Pennsylvania State University, State College, PA 16801, USA
anow at: the Department of Atmospheric Sciences, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, FL 33149, USA
Abstract. The chemical complexity of biomass burning organic aerosol (BBOA) greatly increases with photochemical aging in the atmosphere, necessitating controlled laboratory studies to inform field observations. In these experiments, BBOA from American white oak (Quercus alba) leaf and heartwood samples was generated in a custom-built emissions and combustion chamber and photochemically aged in a Potential Aerosol Mass (PAM) flow reactor. A Thermal desorption Aerosol Gas chromatograph (TAG) was used in parallel with a high-resolution time-of-flight Aerosol Mass Spectrometer (AMS) to analyze BBOA chemical composition at different levels of photochemical aging. Individual compounds were identified and integrated to obtain relative decay rates for key molecular components. A recently-developed chromatogram binning positive matrix factorization (PMF) technique was used to obtain mass spectral profiles for factors in TAG BBOA chromatograms, improving analysis efficiency and providing a more complete determination of unresolved complex mixture (UCM) components. Additionally, the recently characterized TAG decomposition window was used to track molecular fragments created by the thermal decomposition of thermally labile BBOA during sample desorption. We demonstrate that while most components of primary BBOA decrease with photochemical aging, certain components eluting within the TAG thermal decomposition window instead increase. Specifically, the increasing trend in decomposition m / z 44 (CO2+) signals formation of secondary organic aerosol (SOA) in the PAM reactor. Sources of m / z 60 (C2H4O2+), typically attributed to freshly-emitted BBOA in AMS field measurements, were also investigated. From the TAG chemical speciation and decomposition window data, we observed a decrease in m / z 60 with photochemical aging due to the decay of anhydrosugars (including levoglucosan) and other compounds, as well as an increase in m / z 60 due to the formation of thermally labile organic acids within the PAM reactor, which decompose during TAG sample desorption. When aging both types of BBOA (leaf and wood), the AMS data exhibit a combination of these two contributing effects, causing limited change to the overall m / z 60 signal. Our observations demonstrate the importance of chemically-speciated data in fully understanding bulk aerosol measurements provided by the AMS in both laboratory and field studies.

Citation: Fortenberry, C. F., Walker, M. J., Zhang, Y., Mitroo, D., Brune, W. H., and Williams, B. J.: Bulk and Molecular-Level Characterization of Laboratory-Aged Biomass Burning Organic Aerosol from Oak Leaf and Heartwood Fuels, Atmos. Chem. Phys. Discuss.,, in review, 2017.
Claire F. Fortenberry et al.
Claire F. Fortenberry et al.


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Short summary
In these laboratory studies, two types of biomass burning organic aerosol (BBOA) were generated in a combustion chamber and treated in a flow reactor to mimic atmospheric oxidation. Complementary bulk and molecular chemical measurements show that while many species deplete with oxidation, oxidized BBOA markers are enhanced. The results provide insight into the complex chemical evolution of BBOA over nearly 10 days of atmospheric photochemistry, informing future laboratory and field studies.
In these laboratory studies, two types of biomass burning organic aerosol (BBOA) were generated...