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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 9 | Copyright
Atmos. Chem. Phys., 16, 5561-5572, 2016
https://doi.org/10.5194/acp-16-5561-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 04 May 2016

Research article | 04 May 2016

Single-particle characterization of biomass burning organic aerosol (BBOA): evidence for non-uniform mixing of high molecular weight organics and potassium

Alex K. Y. Lee1, Megan D. Willis1, Robert M. Healy2,3,a, Jon M. Wang3, Cheol-Heon Jeong3, John C. Wenger2, Greg J. Evans3, and Jonathan P. D. Abbatt1 Alex K. Y. Lee et al.
  • 1Department of Chemistry, University of Toronto, Toronto, Canada
  • 2Department of Chemistry and Environmental Research Institute, University College Cork, Cork, Ireland
  • 3Southern Ontario Centre for Atmospheric Aerosol Research, Department of Chemical Engineering & Applied Chemistry, University of Toronto, Toronto, Canada
  • anow at: Environmental Monitoring and Reporting Branch, Ontario Ministry of the Environment and Climate Change, Toronto, Canada

Abstract. Biomass burning organic aerosol (BBOA) can be emitted from natural forest fires and human activities such as agricultural burning and domestic energy generation. BBOA is strongly associated with atmospheric brown carbon (BrC) that absorbs near-ultraviolet and visible light, resulting in significant impacts on regional visibility degradation and radiative forcing. The mixing state of BBOA can play a critical role in the prediction of aerosol optical properties. In this work, single-particle measurements from a Soot-Particle Aerosol Mass Spectrometer coupled with a light scattering module (LS-SP-AMS) were performed to examine the mixing state of BBOA, refractory black carbon (rBC), and potassium (K, a tracer for biomass burning aerosol) in an air mass influenced by wildfire emissions transported from northern Québec to Toronto, representing aged biomass burning plumes. Cluster analysis of single-particle measurements identified five BBOA-related particle types. rBC accounted for 3–14wt% of these particle types on average. Only one particle type exhibited a strong ion signal for K+, with mass spectra characterized by low molecular weight organic species. The remaining four particle types were classified based on the apparent molecular weight of the BBOA constituents. Two particle types were associated with low potassium content and significant amounts of high molecular weight (HMW) organic compounds. Our observations indicate non-uniform mixing of particles within a biomass burning plume in terms of molecular weight and illustrate that HMW BBOA can be a key contributor to low-volatility BrC observed in BBOA particles. The average mass absorption efficiency of low-volatility BBOA is about 0.8–1.1m2g−1 based on a theoretical closure calculation. Our estimates indicate that low-volatility BBOA contributes ∼ 33–44% of thermo-processed particle absorption at 405nm; and almost all of the BBOA absorption was associated with low-volatility organics.

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Single-particle measurements from a soot-particle aerosol mass spectrometer were performed to examine the mixing state of aerosol particles in an air mass influenced by aged biomass burning. Our observations indicate non-uniform mixing of particles within a biomass burning plume in terms of molecular weight and potassium content, and illustrate that high molecular weight organic compounds can be a key contributor to low-volatility BrC observed in biomass burning organic aerosols.
Single-particle measurements from a soot-particle aerosol mass spectrometer were performed to...
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