Effects of charring on mass, organic carbon, and stable carbon isotope composition of wood

To aid in understanding black carbon (BC) formation during smoldering combustion in forest fires, we characterized charring of a softwood and hardwood. Charring (150, 340, 480 °C) caused mass loss (7–84%), enrichment of organic carbon (OC) (0–32%), and 13C depletion (>150 °C). As determined by 13C MAS NMR, the OC composition of the woods was dominated by (di)-O-alkyl structures, and the chars by alkyl and aromatic structures. With increasing temperature, aromatic structures increased and the chars became more similar, although initial differences in OC concentration and δ13C of woods persisted. The BC cluster sizes apparently remained small, pointing towards a low resistance against oxidation.