Investigating the Nighttime Chemistry of Biomass Burning Emissions

The nighttime chemistry of biomass burning (BB) plumes has the potential to strongly influence air quality but is completely unknown. As part of the Fire Influence on regional and Global Environments Experiment (FIREX), we propose a multi-investigator collaboration to elucidate the nighttime gas- and particle-phase chemistry in BB plumes. We hypothesize such chemistry is driven by as yet unexplored reactions between nocturnal oxidants (e.g., ozone (O₃), nitrate radical (NO₃), and dinitrogen pentoxide (N₂O₅)), with smoldering emissions (e.g., terpenes, oxygenated aromatics, and particulate matter (PM)). To address our hypothesis and provide critical insight into nighttime BB plume chemistry, we will apply the following advanced analytical techniques, in close coordination with other FIREX investigators: 1) two dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS) for characterization of gaseous emissions and initial transformation products of non- methane organic compounds (NMOCs); 2) cavity ring-down spectroscopy (CRDS) for NO₃, N₂O₅ and other reactive nitrogen species; 3) open-path Fourier transfer infrared spectroscopy (OP-FTIR) for O₃, nitrogen oxides, nitrous acid, ammonia, peroxyalkyl nitrates, light NMOCs, and total terpenes; and 4) photoacoustic extinctiometers (PAX) for brown carbon (BrC) measurements. We will carry out these measurements in a four-phase plan, participating in both laboratory and field studies during FIREX. The set of proposed measurements will provide the most comprehensive emissions inventories and speciation profiles recorded to date, together with observational constraints from laboratory and field studies intended for development of a complete model representation of nighttime BB chemistry.

This proposed research is a key component of the broader effort to understand BB emissions and chemistry envisioned for FIREX. Specific deliverables and outcomes will include: a publicly available database of NMOCs emitted from North American fuels (molecular-level identification and quantification); characterization of nighttime secondary PM production potential (including BrC) in BB plumes; assessment of the influence of nighttime BB plume chemistry on next-day O₃ production potential; and recommendations for improved model representation of nighttime chemistry in predictive regional models. Nighttime processes currently are a major uncertainty for models of BB-derived O₃ and PM and therefore a limiting factor for accurate predictions of the influences of fire on air quality and climate. The proposed research thus will directly support NOAA’s long term goals in the area of climate adaptation and mitigation (“improved scientific understanding of the changing climate system and its impacts”) and a weather ready nation (“healthy people and communities due to improved air and water quality services”) as articulated in NOAA’s Next Generation Strategic Plan.