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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Sep 2018

Research article | 05 Sep 2018

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Atmospheric Evolution of Molecular Weight Separated Brown Carbon from Biomass Burning

Jenny P. S. Wong1, Maria Tsagaraki2, Irini Tsiodra2,3, Nikolaos Mihalopoulos2,4, Kalliopi Violaki5, Maria Kanakidou2, Jean Sciare6, Athanasios Nenes1,3,4,7, and Rodney J. Weber1 Jenny P. S. Wong et al.
  • 1Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, 30331, USA
  • 2Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, 71003 Heraklion, Greece
  • 3ICE-HT, Foundation for Research and Techno logy Hellas, Patras, 26504, Greece
  • 4IERSD, National Observatory of Athens, Palea Penteli, 15236, Greece
  • 5Aix-Marseille University, Mediterranean Institute of Oceanography (MIO) UMR 7294, University de Toulon, CNRS, IRD, France
  • 6Energy Environment and Water Research Center, The Cyprus Institute, Nicosia 1645, Cyprus
  • 7School of Architecture, Civil & Environmental Engineering, École Polytechnique Fédérale de Lausanne, Lausanne, 1015, Switzerland

Abstract. Biomass burning is a major source of atmospheric brown carbon (BrC) and through its absorption of UV/VIS radiation, it can play an important role on the planetary radiative balance and atmospheric photochemistry. The considerable uncertainty of BrC impacts is associated with its poorly constrained sources, transformations and atmospheric lifetime. Here we report laboratory experiments that examined changes in the optical properties of the water-soluble BrC fraction of biomass burning particles. Effects of direct UVB photolysis and OH oxidation in the aqueous phase on molecular weight-separated BrC were studied. Results indicated that low molecular weight (MW) BrC (< 400 Da) was rapidly photobleached by both direct photolysis and OH oxidation on an atmospheric timescale of approximately 1 hour. High MW BrC (≥ 400 Da) underwent initial photoenhancement over a few hours, followed by slow photobleaching over ~ ten hours. The laboratory experiments were supported by observations from ambient BrC samples that were collected during the fire seasons in Greece. These samples, containing freshly emitted to aged biomass burning aerosol, were analyzed for both water and methanol soluble BrC. Consistent with the laboratory experiments, high MW BrC dominated the total light absorption at 365 nm for both methanol and water-soluble fractions of ambient samples with atmospheric transport times of 1 to 68 hours. These ambient observations indicate that overall, biomass burning BrC across all molecular weights have an atmospheric lifetime of 15 to 20 hours, consistent with estimates from previous field studies – although the BrC associated with the high MW fraction remains relatively stable and is responsible for light absorption properties of BrC throughout most of its atmospheric lifetime. For ambient samples of aged (> 10 hours) biomass burning emissions, poor linear correlations were found between light absorptivity and levoglucosan, consistent with other studies suggesting a short atmospheric lifetime for levoglucosan. However, a much stronger correlation between light absorptivity and total hydrous sugars was observed, suggesting that they may serve as more robust tracers for aged biomass burning emissions. Overall, the results from this study suggest that robust model estimates of BrC radiative impacts require consideration of the atmospheric aging of BrC and the stability of high-MW BrC.

Jenny P. S. Wong et al.
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Status: final response (author comments only)
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Jenny P. S. Wong et al.
Jenny P. S. Wong et al.
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Publications Copernicus
Short summary
Biomass burning is a major source of light absorbing organic species in atmospheric aerosols and they can play an important role on climate and atmospheric chemistry. Through a combination of laboratory experiments and field observations, this work demonstrated that the light absorption properties of aged biomass burning organic aerosols are dominated by high molecular weight compounds. In addition, we found that total hydrated sugars may be a robust tracer for aged biomass burning aerosols.
Biomass burning is a major source of light absorbing organic species in atmospheric aerosols and...