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Volume 18, issue 13 | Copyright
Atmos. Chem. Phys., 18, 9263-9281, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 Jul 2018

Research article | 03 Jul 2018

High- and low-temperature pyrolysis profiles describe volatile organic compound emissions from western US wildfire fuels

Kanako Sekimoto1,2,3,*, Abigail R. Koss1,2,4,a,*, Jessica B. Gilman1, Vanessa Selimovic5, Matthew M. Coggon1,2, Kyle J. Zarzana1,2, Bin Yuan1,2,6, Brian M. Lerner1,2,b, Steven S. Brown1,4, Carsten Warneke1,2, Robert J. Yokelson5, James M. Roberts1, and Joost de Gouw1,2,4 Kanako Sekimoto et al.
  • 1NOAA Earth System Research Laboratory (ESRL), Chemical Sciences Division, Boulder, CO 80305, USA
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO 80309, USA
  • 3Graduate School of Nanobioscience, Yokohama City University, Yokohama, Kanagawa 236-0027, Japan
  • 4Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, CO 80302, USA
  • 5Department of Chemistry, University of Montana, Missoula, MT 59812, USA
  • 6Institute for Environment and Climate Research, Jinan University, Guangzhou, China
  • anow at: Department of Civil & Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02142, USA
  • bnow at: Aerodyne Research, Inc., Billerica, MA 01821, USA
  • *These authors contributed equally to this work.

Abstract. Biomass burning is a large source of volatile organic compounds (VOCs) and many other trace species to the atmosphere, which can act as precursors to secondary pollutants such as ozone and fine particles. Measurements performed with a proton-transfer-reaction time-of-flight mass spectrometer during the FIREX 2016 laboratory intensive were analyzed with positive matrix factorization (PMF), in order to understand the instantaneous variability in VOC emissions from biomass burning, and to simplify the description of these types of emissions. Despite the complexity and variability of emissions, we found that a solution including just two emission profiles, which are mass spectral representations of the relative abundances of emitted VOCs, explained on average 85% of the VOC emissions across various fuels representative of the western US (including various coniferous and chaparral fuels). In addition, the profiles were remarkably similar across almost all of the fuel types tested. For example, the correlation coefficient r2 of each profile between ponderosa pine (coniferous tree) and manzanita (chaparral) is higher than 0.84. The compositional differences between the two VOC profiles appear to be related to differences in pyrolysis processes of fuel biopolymers at high and low temperatures. These pyrolysis processes are thought to be the main source of VOC emissions. High-temperature and low-temperature pyrolysis processes do not correspond exactly to the commonly used flaming and smoldering categories as described by modified combustion efficiency (MCE). The average atmospheric properties (e.g., OH reactivity, volatility, etc) of the high- and low-temperature profiles are significantly different. We also found that the two VOC profiles can describe previously reported VOC data for laboratory and field burns.

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We found that on average 85 % of the VOC emissions from biomass burning across various fuels representative of the western US (including various coniferous and chaparral fuels) can be explained using only two emission profiles: (i) a high-temperature pyrolysis profile and (ii) a low-temperature pyrolysis profile. The high-temperature profile is quantitatively similar between different fuel types (r2 > 0.84), and likewise for the low-temperature profile.
We found that on average 85 % of the VOC emissions from biomass burning across various fuels...