Organic tracers in aerosols from the residential combustion of pellets and agro-fuels

The consumption of pellets and alternative biofuels, such as some agricultural residues, has experienced a tremendous growth in Mediterranean countries, which has changed the panorama of biomass burning emissions. To apply source apportionment models, specific chemical signatures for smoke aerosols are necessary. In this study, filter samples of fine particles (PM2.5) from the combustion of four different types of pellets and three agro-fuels (shell of pine nuts, olive pit and almond shell) in a pellet stove were collected. The PM2.5 samples were extracted with dichloromethane/methanol and the dried extracts were silylated before injection into the gas chromatograph-mass spectrometer (GC-MS). The analysis included monosaccharide anhydrides, resin acids, methoxyphenols and sterols. The amounts emitted were highly variable and dependent on both biofuel and combustion temperature. On average, the anhydrosugar particle mass fractions for the seven biofuels were 30 to 70 times lower than the values reported for manually fired systems. The highest levoglucosan emissions were observed for olive pit. Levoglucosan to mannosan ratios ranged from values around 2 for pellets and shell of pine nuts to much higher quotients, similar to those reported for hardwood combustion. Irrespective of biofuel, vanillin and vanillic acid were always present in the smoke samples. Coniferyl alcohol was only detected in samples from the combustion of olive pit and pellets with the highest softwood content. Sinapyl alcohol was exclusively emitted by olive pit. Dehydroabietic and isopimaric acids were represented in emissions whether from all type of pellets or from shell of pine nuts, whilst abietic acid was only quantifiable in PM2.5 from the combustion of pellets made of coniferous wood. Sitosterol was solely detected in smoke particles from shell of pine nuts and olive pit.