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.