UC Riverside

The increase in the frequency, extent, and duration of wildfires has become a great concern for air quality and climate because of the significant quantities of trace gases released from biomass burning (BB). Once in the atmosphere, BB emissions have a strong influence on climate, tropospheric chemistry, and human health. Advances in analytical techniques have recently enabled improved identification and quantification of the gas-phase emissions from BB, including volatile organic compounds (VOCs). A few classes of these BB-derived VOCs have been identified as ozone (O3) and secondary organic aerosol (SOA) precursors but their reactions in the atmosphere generally are poorly understood and/or are inadequately represented in air quality models. Such classes of VOCs include heterocyclic compounds (e.g., furans), oxygenated aromatics (e.g., phenols), and monoterpenes (e.g., camphene). As presented in this dissertation, the Statewide Air Pollution Research Center (SAPRC) modeling system was used to develop new chemical mechanisms and to conduct mechanistic studies of O3 and SOA formation from these understudied VOCs emitted from BB. New gas-phase chemical mechanisms were derived for furans, phenols, and their major oxidation products based on published experimental data, molecular modeling simulations, and estimations from the SAPRC mechanism generation system (MechGen). The new mechanisms were implemented into the SAPRC box model and evaluated based on model-measurement comparisons of VOC consumption, nitric oxide (NO) decay, O3 formation, and radical levels. The mechanisms were developed with no tuning to fit the experimental data used for evaluation and showed much better model performance compared to the previous versions of mechanisms in simulating chamber experiments for furans and phenols (except for 2,4-dimethylphenol). MechGen was also used to derive a chemical mechanism for camphene that was applied in the SAPRC box model to investigate the role of peroxy radicals (RO2) in camphene SOA formation. In the chamber experiments, an unexpected enhancement of SOA formation was observed at higher NOx levels. SAPRC simulation results suggested that the higher SOA mass yields at higher initial NOx levels were primarily due to higher production of RO2 and the generation of highly oxygenated organic molecules (HOMs). Camphene RO2 reacts with NO and the resultant RO2 undergo hydrogen (H)-shift isomerization reactions in the presence of NOx, leading to the formation of HOMs which have significantly lower volatilities than products formed via other pathways. The research presented in this dissertation has advanced the understanding of gas-phase chemistry for BB-derived VOCs including furans, phenols, and camphene while also addressing inadequate representations of these compounds in chemical models. For the first time, the chemically detailed SAPRC box model was used to establish the connection between gas-phase chemistry and SOA formation. The findings in this dissertation have aided in the optimization of MechGen estimation methodology and have made it more visible and accessible to the atmospheric chemistry community.