Synthesis and characterisation of laboratory-charred grass straw ( Oryza sativa) and chestnut wood ( Castanea sativa) as reference materials for black carbon quantification

Abstract

We synthesised large (∼2 kg) quantities of two chars for use as commercially available reference materials for the quantification of black carbon (BC). We pyrolysed chestnut wood ( Castanea sativa) and grass straw ( Oryza sativa) at 450 °C under a N 2 atmosphere, which mimics the oxygen-free conditions on the inside of burning material at a moderate burning temperature. The charred materials were dominated by aromatic carbon (∼70%), had low H/C (∼0.7) and O/C (∼0.3) ratios and low surface areas (2–6 m 2 g −1). Isotopic changes on charring were small (⩽0.3‰). In these respects, the synthesised chars were similar to chars produced at low temperature (<500 °C) in natural fires and thus may prove to be appropriate materials for calibrating BC quantification methods. Both chars have been used in a comparative study of BC quantification.