Highly Speciated Measurements of Terpenoids Emitted from Laboratory and Mixed-Conifer Forest Prescribed Fires

Wildland
fires in the western United States are projected to increase
in frequency, duration, and size. Characterized by widespread and
diverse conifer forests, burning within this region may lead to significant
terpenoid emissions. Terpenoids constitute a major class of highly
reactive secondary organic aerosol (SOA) precursors, with significant
structure-dependent variability in reactivity and SOA-formation potential.
In this study, highly speciated measurements of terpenoids emitted
from laboratory and prescribed fires were achieved using two-dimensional
gas chromatography. Nearly 100 terpenoids were measured in smoke samples
from 71 fires, with high variability in the dominant compounds. Terpenoid
emissions were dependent on plant species and tissues. Canopy/needle-derived
emissions dominated in the laboratory fires, whereas woody-tissue-derived
emissions dominated in the prescribed fires. Such differences likely
have implications for terpenoid emissions from high vs low intensity
fires and suggest that canopy-dominant laboratory fires may not accurately
represent terpenoid emissions from prescribed fires or wildland fires
that burn with low intensity. Predicted SOA formation was sensitive
to the diversity of emitted terpenoids when compared to assuming a
single terpene surrogate. Given the demonstrated linkages between
fuel type, fire terpenoid emissions, and the subsequent implications
for plume chemistry, speciated measurements of terpenoids in smoke
derived from diverse ecosystems and fire regimes may improve air quality
predictions downwind of wildland fires.