Wednesday, November 15, 2006 - 10:15 AM
281-5
Molecular Characterization of Black Carbon from Reference Soils and Fire Affected Soils by Pyrolytic, Spectroscopic and Thermogravimetric Techniques.
Despite the considerable efforts to characterize sedimentary organic carbon, and the significant improvements achieved in the analytical techniques, a large fraction of it remains biochemically uncharacterised. To this fraction belongs the so-called Black Carbon (BC), a form of refractory organic matter (ROM) produced by the incomplete combustion of fossil fuels and vegetation widely distributed in environmental matrices including soils. There are currently well-known ambiguities concerning the potential origin and occurrence of BC, which is not a pure substance but rather a “continuum” of materials with different physicochemical properties. In fact, the isolation of BC presents serious experimental constrains, and a standardized and accepted method of measuring and characterizing BC does not exist despite the urgency to improve global terrestrial and sedimentary carbon accounting and to adjust carbon fluxes. In this communication the structural features of BC from two soils (Chernozemic mollisol and Wiessenboden vertisol) and two related materials (grass and charred wood) recommended by the BC Ring-Trial were compared with those of BC from a selection of fire affected soils from Andalusian Mediterranean forests. Different analytical methods were used to characterize the BC molecular structure contained in the samples. Correspondence was observed between samples resistant to high oxidation temperature during thermogravimetric experiments and their aromatic content as estimated by the 13C NMR integration regions. Pyrolysis-GC/MS analysis was useful in detecting typical fire derived markers in BC like material rich samples. Characteristic peaks were also identified which may have a marker value to distinguish among different BC materials.
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