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.