P392-TH A NEW CONCEPTUAL MODEL FOR THE STRUCTURAL PROPERTIES OF CHAR PRODUCED DURING VEGETATION FIRES

After vegetation fires considerable amounts of charred necromass are incorporated into soils and sediments. To elucidate its role in geobiochemical cycles a good understanding of its chemistry is crucial. Although several models describing char on a molecular level are reported in the literature (Schmidt & Noack, 2000), a commonly accepted view of the chemistry involved in Black Carbon (BC) production during vegetation fires is still missing. Therefore, the intention of the present work was to obtain some insights into structural properties of char produced during biomass burning by comparing results obtained from controlled charring experiments, the analysis of naturally charred soil organic matter with the pyrolysis literature. Our studies indicate that the aromatic skeleton of char accumulating after a vegetation fire must contain remains of the lignin backbone and considerable contributions of furans and anhydrosugars from thermally altered cellulose. Since heating of vegetation residues leads to little changes of their C/N ratios in the charred product, N must be incorporated into structures which are fairly resistant to heating. Solid-state 15N NMR spectroscopy identified them as mostly pyrrole/indole-type N with minor contribution of pyridine N. Depending on the sourc