Rapid and economical quantification of black carbon in soils using a modified benzene polycarboxylic acids (BPCA) method

Abstract

Black carbon, the ubiquitous stable product of incomplete combustion, is a potential sink for atmospheric CO2 and, therefore, a contributor to the Earth’s radiative heat balance. Accurate information about the distribution of black carbon in soils is important for climate change projections, given that the black carbon content of soils varies widely across the globe. In response to this issue, an accurate, rapid and cost-effective method to assess BC is needed. The use of benzene polycarboxylic acids (BPCA) as molecular markers of black carbon has the advantage of specifically tracking the polyaromatic backbone of the black carbon continuum. However, this method has three major disadvantages: (a) it is expensive; (b) it is very time-consuming; and (c) some of the literature states that care has to be taken when applying the BPCA method to organic-rich matrices. In response to these disadvantages, the aims of the present study were: (a) to check the validity of a new shorter and economical method for black carbon quantification based on BPCA as molecular markers; and (b) to study the correlation between BPCA formation during the analysis and the soil sample’s OC content. The proposed method for black carbon quantification is based on the BPCA method developed by Glaser et al. (1998), but uses a simple direct elemental analysis (EA) of C content in the residue obtained after a strong digestion instead of the molecular determination by gas chromatography with flame ionisation detector (GC-FID). This simplification of the method represents a great cost reduction (in time and expense) providing a rapid and accurate method for large soil sample sets.