CAS-Climate: Interfacial Reactions of Model Wildfire and Combustion Emissions (ALN 47.083)

Interfacial Reactions of Model Wildfire and Combustion Emissions Project Summary Overview Biomass burning and combustion emissions release reactive phenolic aldehydes to the atmosphere, which form secondary organic aerosols and in consequence can reduce visibility, deteriorate air quality, and affect climate. The project’s objective is to develop transformative understanding of interfacial chemical mechanisms that alter the composition, and consequently the physicochemical properties, of atmospheric particles. The research will examine key reactions driven by nighttime atmospheric oxidants, including nitrate radicals (NO3), ozone (O3), and hydroxyl radicals (HO•) which attack the surface-active phenolic aldehydes at the interface of water and air. Selected phenolic aldehydes (syringaldehydes, vanillin, and 4- hydroxybenzaldehyde) that are ubiquitous in the atmosphere resulting from biomass burning and combustion emissions will serve as models to distinguish heterogenous production pathways of chromophoric molecules, including nitrophenols. An interdisciplinary approach using multiple analytical instruments and reactors will facilitate the investigation of oxidation mechanisms. Real time experiments using OESI-MS, UV-visible, and FTIR spectroscopies will be supplemented by off-line chromatographic and mass spectrometry analyses (ion chromatography-conductivity-MS, UHPLC-UV-ESI-MS, GC-MS, GC-TCD-FID, GC-FID, etc.), and other techniques (cyclic voltammetry, fluorescence, NMR). This approach includes (1) identifying chemical structures, (2) monitoring reaction kinetics with and without radical traps, and (3) determining kinetic isotope effects, which will inform the rate determining step for the incorporation of chromophores, volatility of products, and the key tropospheric intermediates. Intellectual Merit The study of reactions on the interface of water and air is at the forefront of atmospheric chemistry research to understand the fate of biomass burning and combustion pollution. The following questions will be tackled from a physical and organic chemistry perspective: 1) How is the interfacial oxidation of phenolic aldehydes initiated under environmental levels of O3 and NO3 to produce reactive species that form coupling oligomers and nitrophenols in the troposphere? 2) How is the interfacial reactivity affected by the presence of competing radical scavengers (e.g., para-phthalic acid), reactive halogens species (e.g., iodide), or heavy water? Can the contribution of different reactive intermediates toward the generation of nitrophenols be discriminated with selective radical traps? What are the effects of varying the concentration of phenols, temperature, and pH on the nitration at the air-water interface? 3) What factors favor or disfavor competing nitration and coupling reactions of phenolic aldehydes at the air-water interface? What is the absorption enhancement and its temperature variation for model organic matter generated in the presence of tropospheric relevant electrolytes? Answering these questions will provide transformative understanding of the mechanisms by which the oxidation of phenolic aldehydes proceeds at environmental interfaces. The fundamental knowledge to be generated will advance other areas of science and engineering because the study of reactions on the surface of water is relevant to many other environmental, technological, and biochemical processes. Overall, the proposed research is closely aligned to the goals of the Environmental Chemical Sciences Program by providing molecular scale understanding of transformations on environmental surfaces. Broader Impacts The project will advance the scientific understanding of the interfacial processing of pollutants from biomass burning and combustion emissions with direct implications to air quality, public health, and climate. The new knowledge generated will explain the ubiquitous formation of sunlight absorbing species of low volatility capable of forming tropospheric aerosol. The PI (Guzman) as a Hispanic faculty will continue inspiring, educating, and training students in the state of Kentucky, acting as a role model for underrepresented science students. Three educational activities are proposed: 1) Broadening the participation of underrepresented graduate and undergraduate students. The unique atmospheric environmental chemistry research and education program in the state of Kentucky will continue active for training the next generation of graduate and undergraduate students with a plan that prioritizes the recruitment of underrepresented minorities. 2) Fostering the integration of research and education by continuing teaching Environmental and Analytical Chemistry courses. 3) Organizing a hands-on workshop for K-12 students of Tates Creek Elementary School, a powerful educational tool about the use of analytical instrumentation and technologies used to study the environment. Guzman