Abstracts Chemistry

EMISSION AND CHEMISTRY OF VOLATILE ORGANIC COMPOUNDS IN WESTERN U.S. WILDIFRE SMOKE

by Wade Jeremy Permar

Wildfires are a significant source of volatile organic compounds (VOCs) in the western U.S., emitting hundreds to thousands of different species that play key roles in tropospheric oxidation, ozone production, and secondary organic aerosol formation. Many of these VOCs have only recently been identified and quantified in laboratory burning experiments. Consequently, little is known about their emissions from wildfires, which species are most important for plume OH oxidation chemistry, and how they evolve as smoke plumes age. This dissertation aims to improve our understanding of the emissions and chemistry of VOCs in wildfire smoke using detailed in situ measurements made during the summer 2018 Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) field campaign. WE-CAN sampled wildfire smoke across seven western states and is one of the most comprehensive field studies of smoke emissions and aging to date. During the campaign, VOCs were measured by four complementary instruments, which were all found to agree within their stated uncertainties for most co-measured species. Leveraging these measurements, we report emission factors (EFs) and emission ratios (ERs) for 161 VOCs measured from 24 individual fires (Permar et al., 2021). OH reactivity (OHR) was used to determine which species are most important for daytime plume OH chemistry, and therefore should be included in next generation atmospheric chemistry models. From this, the master chemical mechanism was determined to contain chemistry for most reactive species. However, ~50 % of the emitted VOC OHR is not currently implemented in the commonly used GEOS-Chem chemical transport model. Implementing chemistry for furan-containing species, butadienes, and biomass burning monoterpenes would greatly improve model representation (Permar et al., 2023). As smoke plumes age, formic acid was rapidly produced at rate of 2.7 ppb ppmCO-1 h-1, resulting in it and acetic acid become an increasingly important OH sink in aged smoke. GEOS-Chem generally underestimates their enhancement during WE-CAN, likely due to missing secondary production from wildfire and biogenic emissions. Collectively, this work significantly expands our understanding of western U.S. wildfire emissions while providing direction for future model and emission inventory development.