RUI: Far Ultra-Violet (172 nm) Photolysis of Gaseous Anthropogenic Pollutants

1. OVERVIEW Volatile organic compounds (VOCs) are emitted from a range of natural and anthropogenic sources, the latter including electrical power generation, transportation, waste recycling, chemical manufacture, processing and solvents use. VOCs are intricately involved in the photochemical processes in the atmosphere leading to formation of ozone (O3), particulate matter and photochemical smog, all of top concerns regarding human health and exposure risks. Recent technological developments to reduce anthropogenic emissions of VOCs have focused on the utilization of ultraviolet (UV) and vacuum ultra violet (VUV) degrade and eliminate environmental gaseous pollutants. The proposed project aims to be the first concerted effort to investigate the photochemical processes occurring in response to 172 nm ultraviolet radiation treatment of emissions and industrial processing-exhaust. Experiments will provide direct measurements of Far-UV (120-200 nm) absorption cross-sections, photolysis quantum yields, and stable end-products with the goal of developing a photolysis and photochemical reaction mechanism for a set of model compounds. The experiments will be conducted in an advanced photochemical simulation chamber, developed as part of this project. Measurements will be performed as a function of pressure and temperature, and involve chemical analysis by IR and UV spectrophotometric methods. Far-UV spectra and absorption cross-sections will be measured on an analytical UV spectrophotometric bench. The proposed experiments will engage undergraduate students in several self-contained laboratory research projects, designed to build upon each other and all to provide publishable results. This research is necessary to understand the Far-UV photochemistry of the pollutants and to further this method as a pollution abatement strategy. This proposal is submitted to NSF 18-561 - Division of Chemistry: Disciplinary Research Programs, Unit CHE - Environmental Chemical Science. 2. INTELLECTUAL MERIT OF THE PROPOSED ACTIVITY The main emission output from typical mercury based UV lamps is centered around 254 nm with a smaller contribution at 185 nm. Recently, excimer lamps producing 172 nm radiation have become commercially available. This Far-UV radiation efficiently produces O1(D) and OH radicals, which initiate known photochemical degradation mechanisms for the VOCs. However, these high energy UV photons can also directly photolyze VOCs at high efficiencies. Very little is known in the literature regarding the quantum yields and mechanisms for VOCs degradation initiated at Far-UV wavelengths (region between the Lyman-alpha band and ~200 nm). To properly assess the Far-UV photolysis rates, high resolution cross-sections are needed at the appropriate wavelengths, but VOCs have typically only been studied in the context of photochemistry at actinic wavelengths. Moreover, the few VOCs for which VUV spectra can be found in the literature, their measured absorption cross-sections often differ by a factor of 2 or larger. This proposed project will advance our knowledge of the VUV photochemistry of key atmospheric anthropogenic pollutants by providing detailed information on the absorption cross-sections, quantum yields and degradation products. 3. BROADER IMPACT OF THE PROPOSED ACTIVITY The data produced in this research will contribute to our effort addressing critical issues of air pollution and human and environmental health, and is likely to garner interest from the environmental science community, as well as the general society. In addition, the research activities described above is designed to enhance undergraduate students? learning experience, preparing them for advanced degrees in, and future careers related to, the chemical sciences. Part of the requested funds will directly support student involvement in instrument development, publishable fundamental and applied research and dissemination of results.