COMPOUND-SPECIFIC ISOTOPE ANALYSIS OF FATTY-ACIDS AND POLYCYCLIC AROMATIC-HYDROCARBONS IN AEROSOLS - IMPLICATIONS FOR BIOMASS BURNING

Fatty acids and polycyclic aromatic hydrocarbons (PAH) have been inves tigated as potential tracer species for the products of biomass burnin g. Fatty acids extracted from unburned sugar cane plants and from part iculate aerosols collected during laboratory burns of sugar cane under smoldering and flaming conditions have been chemically and isotopical ly characterized by gas chromatography-mass spectrometry (GC-MS) and g as chromatography-isotope ratio mass spectrometry (GC-IRMS), respectiv ely. Fatty acids and PAH produced during the burning of a sugar cane f ield in South Africa were similarly characterized. The fatty acids ide ntified in the aerosols collected above the fire were saturated even-c hain species ranging from C12 to C22. The carbon isotopic signatures o f the fatty acids ranged between -19.9 parts per thousand and -23.6 pa rts per thousand, and were more depleted in C-13 than the bulk sugar c ane plant (-12.9 parts per thousand) and the total lipid extract (-17. 9 parts per thousand). The isotopic signatures of the individual fatty acids were conserved during the smoldering laboratory burn. However, the fatty acids collected during the flaming burn showed a depletion o f 1 parts per thousand to 6 parts per thousand relative to the fatty a cids extracted from the unburned plant. This observed depletion was ev en greater for the fatty acids obtained from the sugar cane field burn . Low levels of various PAH were identified in aerosols from the labor atory burns. Phenanthrene, fluoranthene and pyrene obtained from the h eld burn aerosols were isotopically depleted relative to the bulk lipi d material, with carbon isotopic signatures ranging from -22.9 parts p er thousand to -25.4 parts per thousand. The alterations in the isotop ic compositions of fatty acids that occur during combustion provide va riables by which bum-derived compounds can be distinguished from those produced from aeolian transport of detrital vegetative matter. The co mbination of fatty acid isotopic data and PAH data may allow a better understanding of the relative contributions of biogenic and anthropoge nic source materials to aerosols. Copyright (C) 1996 Elsevier Science Ltd.