Benzenepolycarboxylic acids (BPCAs), the molecular structures shown here, are formed during fire and their inherent presence in fire-affected waters may impact dissolved black carbon measurements.
Dissolved black carbon (DBC) is the condensed aromatic fraction of dissolved organic matter produced during wildfire and the burning of biomass. In our lab, we measure DBC concentrations following the benzenepolycarboxylic acid (BPCA) method, which oxidizes condensed aromatic carbon to BPCA molecular markers for quantification. Since “free” BPCA molecules have been identified in fire-affected surface waters and in leachates of burned soils and wildfire ash, we were curious to know if the free BPCAs would survive the sample preparation and analytical procedures, thus contributing to overall DBC concentrations.
A new paper, led by Riley Barton, shows that free BPCAs could be recovered in detectable amounts, with the most-substituted BPCAs (with 5 and 6 carboxylic acid groups) having lower percent recoveries than less-substituted BPCAs (with 3 and 4 carboxylic acid groups). The paper is entitled “The presence of free benzenepolycarboxylic acids (BPCAs) may result in the overestimation of dissolved black carbon in aqueous samples” and was published in the journal Organic Geochemistry. We conclude that DBC quantification could be impacted by free BPCAs in aqueous samples, but the degree of impact is largely dependent upon the properties of the individual BPCA molecular marker and conversion factors used.
