Variability of stable carbon isotopic compositions in individual fatty acids from combustion of C4 and C3 plants: implications for biomass burning

The isotopic characterization of trace organic species produced during biomass burning may allow a better understanding of the source and fate of combustion-derived organic matter. In order to assess the utility of compound specific isotope analysis (CSIA) of fatty acids as a means to distinguish the sources of these species in atmospheric aerosols, the isotopic signatures of fatty acids extracted from unburned C-4 and C-3 vegetation have been determined. Carbon isotopic signatures of fatty acids from unburned C-4 vegetation ranged from -21.1 parts per thousand to -28.2 parts per thousand, whereas those from C-3 vegetation ranged from -32.4 parts per thousand to - 38.5 parts per thousand. Fatty acids isolated from aerosols produced during controlled laboratory burns of C-4 vegetation showed an isotopic depletion of 2 parts per thousand to 6 parts per thousand relative to those extracted from the unburned plant. However, the opposite relationship was observed for C-3 vegetation, with the aerosol fatty acids exhibiting and isotopic enrichment of 2 parts per thousand to 7 parts per thousand relative to those from the unburned plant. Combustion-derived fatty acids may be distinguished from those species that arise from erosion of unburned plant debris. CSIA of fatty acids produced during field burns of C-4 and C-3 vegetation suggests that isotopic characterization of these species in atmospheric aerosols may be useful in determining the fate of organic matter produced during biomass burning. (C) 1998 Elsevier Science B.V. All rights reserved.