Modification of the weak nitric acid digestion method for the quantification of black carbon in organic matrices

The weak nitric acid digestion method (also known as KMD) is a method to quantify black carbon (BC) in mineral soil. Here we extended the use of this methodology from mineral samples to organic matrices. We tested this methodology on known mixtures of pyrolyzed pine wood and needles (at 300 °C and 550 °C) and non-pyrolyzed pine needles and measured: (1) the fraction of pyrolyzed material identified as BC by the methodology, (2) the fraction of non-pyrolyzed pine needles identified as BC, and (3) the precision of the method. We found that the fraction of pyrolyzed-C identified as BC ranges from 10% (needles at 300 °C) to 90% (wood at 550 °C), indicating that the weak nitric acid digestion method can be extended to measure BC in organic matrices and that the methodology can be used in studies aimed to quantify BC stocks in post-fire environments.