Articles | Volume 13, issue 5
Atmos. Chem. Phys., 13, 2415–2422, 2013
Atmos. Chem. Phys., 13, 2415–2422, 2013

Research article 01 Mar 2013

Research article | 01 Mar 2013

Brown carbon absorption linked to organic mass tracers in biomass burning particles

D. A. Lack2,1, R. Bahreini2,1,*, J. M. Langridge2,1, J. B. Gilman2,1, and A. M. Middlebrook1 D. A. Lack et al.
  • 1NOAA Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80304, USA
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado, 216 UCB, Boulder, CO 80309, USA
  • *now at: the University of California, Riverside, CA, 92521, USA

Abstract. Traditional gas and particle phase chemical markers used to identify the presence of biomass burning (BB) emissions were measured for a large forest fire near Boulder, Colorado. Correlation of the organic matter mass spectroscopic m/z 60 with measured particle light absorption properties found no link at 532 nm, and a strong correlation at 404 nm. Non-black carbon absorption at 404 nm was well correlated to the ratio of the mass fractions of particulate organic matter (POM) that was m/z 60 (f60) to m/z 44 (f44). The f60 to f44 ratio did not fully explain the variability in non-BC absorption, due to contributions of brown carbon (BrC) absorption and absorption due to internal mixing of POM with black carbon (BC). The absorption Ångstrom exponent (ÅAbs) showed a good correlation to f60/f44; however the best correlation resulted from the mass absorption efficiency (MAE) of BrC at 404 nm (MAEPOM-404 nm) and f60/f44. This result indicates that the absorption of POM at low visible and UV wavelengths is linked to emissions of organic matter that contribute to the m/z 60 mass fragment, although they do not contribute to 532 nm absorption. m/z 60 is often attributed to levoglucosan and related compounds. The linear relationship between MAEPOM-404 nm and f60/f44 suggests that the strength of BrC absorption for this fire can be predicted by emissions of f60-related organic matter.

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