Fire condensates and charcoals: Chemical composition and fuel source identification

Abstract

Fire condensates from vegetation and household burnings occur ubiquitously in the environment. Until now, however, it was difficult to estimate their origin and any relation to pyrogenic carbon deposited as charcoal. Our aim here was: (i) to differentiate the chemical composition of fire condensates from charcoal particles, and (ii) to relate this to fuel origins from grass, softwood or hardwood. We analysed δ13C and δ15N isotope composition, lignin-derived phenols, benzene polycarboxylic acids (BPCA) and polycyclic aromatic hydrocarbons (PAH), in lab-produced charcoals and condensates at combustion temperatures of 300, 350, 400, 450, 500 and 600 °C. We found that the BPCA and PAH composition of condensates differed significantly from that of charcoals. Condensates exhibited larger portions of benzene penta- to hexacarboxylic acids (B5CA to B6CA), phenanthrene (p < 0.01) and four-ring PAH (fluoranthene, pyrene, chrysene and benz[a]anthracene, p < 0.01). PAH ratios of indeno[1,2,3-cd]pyrene to benzo[ghi]perylene (IP/(IP + B[ghi]P) and fluoranthene to pyrene (Flua/(Flua + Py) were diagnostic for condensates, but independent from fuel type. Composition of the 1,2-, 1,7- and 2,6|3,5 dimethylphenanthrenes (DMP) was fuel specific, with the ratio of the (1,7 + 2,6|3,5)/(1,2 + 1,7 + 2,6|3,5) isomers separating hardwood (0.2–0.6), from grass (0.6–0.9), and softwood (<0.9), thus enabling the identification of both condensate and charcoal fuel sources.