A new conceptual model for the structural properties of char produced during vegetation fires

The elemental and C-13 nuclear magnetic resonance (NMR) analysis of laboratory prepared char samples from the main plant biopolymers (cellulose, lignin, casein), as well as grass and beech sawdust, indicated a greater chemical heterogeneity of plant derived chars than generally assumed from common black carbon (BC) models. The data support a recent concept proposing char as a heterogeneous mixture of thermally altered biomacromolecules with N, O and likely also S substitutions as common features. In contrast to soot, graphitic polyaromatic domains play a minor role in Such chars. The high resistance of casein against thermal treatment and the low atomic N/C values for grass chars demonstrate the quantitative importance of pyrogenic N. A more detailed consideration is needed if a more realistic view of the role of pyrogenic organic matter (PyOM) in soils and sediments is required. (c) 2008 Elsevier Ltd. All rights reserved.