Environ. Sci. Technol. 2008, 42, 8310–8316
Biomass burning is an important primary source of particles containing biomarker compounds, which are introduced into smoke primarily by direct volatilization/steam stripping and by thermal alteration based on combustion conditions. This study presents comprehensive organic compound source profiles for smoke from controlled burning of green vegetation native to the predominant temperate and semiarid forests of the western United States. Smoke particles were extracted with dichloromethane/methanol (2:1, v/v), and the extracts were analyzed as their TMS derivatives by gas chromatography-mass spectrometry. Carbohydrates were by far the major compound class emitted in smoke particles, encompassing 57-77% of the total extractable organic compounds detected here. Lignin derivatives (5-17%) and diterpenoids (up to 16%) from bleed resins were the next most abundant compound groups observed. The major individual compounds encompassed methylinositols (up to 41%, e.g., pinitol) for conifer smokes, deoxyinositols (up to 32%, e.g., quercitol) for samples containing oak vegetation, and the thermally altered product of cellulose combustion levoglucosan (14-21%). The remaining compound classes,i.e.,n-alkanoicacids,n-alkanols,n-alkanes,triterpenoids, steroids, and polycyclic aromatic hydrocarbons, were present at lower abundances (mostly C20, strong even carbon number predominances (most CPI values >50), and Cmax varying from 22 to 28. The secondary alcohol n-nonacosan10-ol was present as a major component in all conifer smoke extracts (Table SI 2; e.g., Figure SI 1a). This compound has been identified previously as a major component in epicuticular waxes from gymnosperm species (28). In addition, alkanediols were found in most of the smoke samples and they are also indicators of epicuticular waxes derived mainly from conifer vegetation (29). This was confirmed by the insignificant presence of these compounds in the smoke samples of oak savanna and deciduous forest (composites 6 and 7, respectively), which presented as major homologues the C24 and C26 alkanols (e.g., Figure SI 1b). Differently, smoke from green vegetation of Juniper forest had the lowest amount of normal alkanols; however, the concentrations of alkanediols were distinctly high (Table SI 2). The n-alkanoic acids in these samples ranged from C12 to C30 as free acids and from C12 to C32 as the methyl esters, with a typical strong even-to-odd carbon number predominance for n-alkanoic acids (CPI range from 10 to 87) and odd-to-even carbon number predominance for methyl esters (CPI ) 4-22). An exception occurred for the high desert Juniper sample, which presented CPI ) 1, mainly due to the unusual high Cmax value at 15 (Table SI 2). Smoke samples were characterized by a bimodal distribution peaking at C16 with a second Cmax at 22. The presence of lower molecular weight fatty acids (
