Direct Detection of Black Carbon in Soils by Py‐GC/MS, Carbon‐13 NMR Spectroscopy and Thermogravimetric Techniques

Abstract

The amount and compositional characteristics of black carbon in soils (mollisol and vertisol), charred biomass (laboratory produced; rice, chestnut), and soils (southern Spain) affected by forest fire have been determined using a combination of thermogravimetry (TG), TG coupled with isotope ratio mass spectrometry (IRMS), solid state 13C nuclear magnetic resonance (NMR) spectroscopy, and pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS). Samples affected by fire had higher total organic matter content, and this was enriched in aromatic components. Good agreement was observed between the content of refractory organic matter (ROM) determined by TG analysis and the aromatic content measured by 13C NMR. Py‐GC/MS demonstrated the presence of aromatic compounds in samples rich in black carbon, the absence of furans (derived from carbohydrates) in soils affected by fire, and the detection of methoxyphenols (derived from lignin) in artificially charred grass and wood. Some of the characteristic peaks obtained by analytical pyrolysis in combination with TG analysis and NMR 13C spectra could be used as markers in the detection of black carbon. This is the first study in which TG‐differential scanning calorimetry (DSC)‐IRMS has been used to detect black carbon formed during artificial smoldering and natural combustion processes.