Brown carbon absorption linked to organic mass tracers in biomass burning particles D. A. Lack1,2, R. Bahreini1,2,*, J. M. Langridge1,2, J. B. Gilman1,2, and A. M. Middlebrook1 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.
Citation: Lack, D. A., Bahreini, R., Langridge, J. M., Gilman, J. B., and Middlebrook, A. M.: Brown carbon absorption linked to organic mass tracers in biomass burning particles, Atmos. Chem. Phys., 13, 2415-2422, doi:10.5194/acp-13-2415-2013, 2013.