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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 15
Atmos. Chem. Phys., 11, 7669–7686, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 11, 7669–7686, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 01 Aug 2011

Research article | 01 Aug 2011

Chemical and physical transformations of organic aerosol from the photo-oxidation of open biomass burning emissions in an environmental chamber

C. J. Hennigan1, M. A. Miracolo1, G. J. Engelhart1, A. A. May1, A. A. Presto1, T. Lee2, A. P. Sullivan2, G. R. McMeeking3,2, H. Coe3, C. E. Wold4, W.-M. Hao4, J. B. Gilman6,5, W. C. Kuster6,5, J. de Gouw6,5, B. A. Schichtel7, J. L. Collett Jr.2, S. M. Kreidenweis2, and A. L. Robinson1 C. J. Hennigan et al.
  • 1Center for Atmospheric Particle Studies, Carnegie Mellon University, USA
  • 2Department of Atmospheric Science, Colorado State University, USA
  • 3Centre for Atmospheric Science, University of Manchester, UK
  • 4Missoula Fire Sciences Laboratory, US Forest Service, USA
  • 5Earth System Research Laboratory, National Oceanic and Atmospheric Administration, USA
  • 6Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, USA
  • 7National Park Service/CIRA, Colorado State University, USA

Abstract. Smog chamber experiments were conducted to investigate the chemical and physical transformations of organic aerosol (OA) during photo-oxidation of open biomass burning emissions. The experiments were carried out at the US Forest Service Fire Science Laboratory as part of the third Fire Lab at Missoula Experiment (FLAME III). We investigated emissions from 12 different fuels commonly burned in North American wildfires. The experiments feature atmospheric and plume aerosol and oxidant concentrations; aging times ranged from 3 to 4.5 h. OA production, expressed as a mass enhancement ratio (ratio of OA to primary OA (POA) mass), was highly variable. OA mass enhancement ratios ranged from 2.9 in experiments where secondary OA (SOA) production nearly tripled the POA concentration to 0.7 in experiments where photo-oxidation resulted in a 30 % loss of the OA mass. The campaign-average OA mass enhancement ratio was 1.7 ± 0.7 (mean ± 1σ); therefore, on average, there was substantial SOA production. In every experiment, the OA was chemically transformed. Even in experiments with net loss of OA mass, the OA became increasingly oxygenated and less volatile with aging, indicating that photo-oxidation transformed the POA emissions. Levoglucosan concentrations were also substantially reduced with photo-oxidation. The transformations of POA were extensive; using levoglucosan as a tracer for POA, unreacted POA only contributed 17 % of the campaign-average OA mass after 3.5 h of exposure to typical atmospheric hydroxyl radical (OH) levels. Heterogeneous reactions with OH could account for less than half of this transformation, implying that the coupled gas-particle partitioning and reaction of semi-volatile vapors is an important and potentially dominant mechanism for POA processing. Overall, the results illustrate that biomass burning emissions are subject to extensive chemical processing in the atmosphere, and the timescale for these transformations is rapid.

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