Estimation of the Emission Factors of the Oxygenated Organic Compounds Generated via Pyrolysis of Eucalyptus and Pine Biomass

Wood pyrolysis during eucalyptus and pine forest fires causes considerable environmental concern because of the associated release of oxygenated organic compounds (OOCs), such as acetic acid, acetol, and aldehydes. Both estimation of the emission factors (EFs) and mechanistic attribution for these OOCs necessitate pyrolysis conducted under rigorously controlled conditions, specifically, low-temperature regimes and gradual rates in heating protocols, temperature-resolved sampling in pyrolysis gas capturing, and independent contribution evaluation of components-derived OOCs emissionutilizing eucalyptus and pine biomass as substrates. The generation of these OOCs was quantified by means of pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) with dedicated gas detector tubes. As species comparison, the EFs at 260-380 °C for acetic acid, acetol, formaldehyde, and acetaldehyde generated via eucalyptus pyrolysis were determined to be 17.0, 7.5, 14.9, and 3.9 g/kg dry biomass, respectively. The corresponding values for pine pyrolysis were 1.6, 0.6, 11.2, and 3.0 g/kg dry biomass, respectively. According to emissions of independent components, the substantial contribution of acetylated pyranoses within hemicellulose to acetic acid formation was evident, and the elevated acetic acid yield in eucalyptus11-fold higher than that in pinebeing attributed primarily to the high reactivity of its acetylated hemicellulose, with a minor influence from the abundance of acetylated substituents in hemicellulose. Glucose reagent is the exclusive source of acetol, and its formation during eucalyptus pyrolysis differed from the well-known retro-aldol pathway, particularly in the rate-limiting step of enediol-ketone isomerization, which may be modulated by interactions with components specific to eucalyptus, although the identity and its mechanistic factor in the level of elementary reaction remains unknown. Furthermore, aldehydes can be derived from both glucose and xylose reagents in (hemi)-cellulose, and the distinct aldehyde production profiles were attributed to such components of eucalyptus and pine, which exhibit different decomposition behaviors in the pyrolysis stage. These conclusions, serving as baseline reference data under anaerobic pyrolysis conditions, provide valuable insights into analyzing pollutant emissions from intact wildfires in future works.