Brown carbon absorption linked to organic mass tracers in biomass burning particles
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 (f(60)) to m/z 44 (f(44)). The f(60) to f(44) 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 Angstrom exponent (A(Abs)) showed a good correlation to f(60)/f(44); however the best correlation resulted from the mass absorption efficiency (MAE) of BrC at 404 nm (MAE(POM-404) (nm)) and f(60)/f(44). 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 MAE(POM-404) (nm) and f(60)/f(44) suggests that the strength of BrC absorption for this fire can be predicted by emissions of f(60)-related organic matter.