Seminar

Abstract

Climate change is a complex global challenge that requires a nuanced understanding of its many contributing factors. While the primary drivers of climate change are the atmospheric abundances of carbon dioxide and methane, anthropogenic fluorinated trace gases also significantly influence the climate impact of human activity. The Montreal Protocol and its Amendments are widely regarded as benchmarks for policies aimed at reducing the ozone depletion potential (ODP) and global warming of replacement compounds. However, uncertainties persist regarding the environmental fate and impacts of their degradation products, necessitating a better understanding of these pathways to evaluate their broader climatic and environmental implications.

This talk investigates and quantifies the UV photolysis of trifluoroacetaldehyde (CF₃CHO), a key degradation product of anthropogenic hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), and related compounds. UV photolysis of CF₃CHO is a potential atmospheric source of fluoroform (CHF₃, HFC-23), a greenhouse gas with one of the highest known global warming potentials (GWPs) (~13,800 over a 100-year time horizon). A discrepancy between atmospheric observations and reported industrial emissions of CHF₃ suggests the presence of unknown chemical sources or pathways that contribute to its atmospheric abundance. With CF₃CHO experiencing minimal removal by OH and other atmospheric oxidants, UV photolysis is identified as a dominant degradation pathway and provides the only direct mechanism for CHF₃ production via CF₃CHO.

This presentation details laboratory measurements of CF₃CHO photolysis quantum yields and CHF₃ product yields across UV wavelengths (248, 266, 281, and 308 nm) and total pressures (100–678 Torr) in N₂/NO bath gas mixtures relevant to tropospheric and stratospheric conditions. Experimental results obtained using Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) demonstrate significant CHF₃ production at shorter wavelengths, while longer wavelengths yield CHF₃ at reduced, pressure-dependent levels measurable under tropospheric conditions (e.g., 308 nm).

In addition, this talk evaluates CHF₃ formation from CF₃CHO derived from known atmospheric trace species and assesses the contribution of these sources to the observed CHF₃ discrepancy. The significance of CHF₃ formation via the recently measured ozonolysis of HFOs is also examined. These findings provide critical insights for policymakers and researchers focused on mitigating the climate impact of fluorinated compounds.

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Dr. Daniel Van Hoomissen is a research scientist at CIRES and NOAA CSL in the Chemical Processes and Instrument Development program. His research interest focuses on developing experimental and theoretical methods to study the fate and reactivity of anthropogenic pollutants in the gas and solution phases.