Prediction of Global Warming Potentials through Computational Chemistry: Testing Robustness of Methodology through Experimental Comparisons
Paul Blowers and Kyle Hollingshead. Chemical and Environmental Engineering, University of Arizona, PO Box 210011, Tucson, AZ 85721-0011
Global warming is a scientifically based concern regarding addition of natural and anthropogenic based chemicals to the troposphere where the species can trap energy in the infrared region. Predicting global warming potentials requires highly accurate rate constant measurements for the reactions of the chemicals with hydroxyl radicals, which is the first and rate limiting step in environmental degradation. Radiative forcing, the amount of energy that can be captured by the chemicals per square meter of exposed area for a given concentration, requires spectroscopic information about peak locations and intensities, which are then aggregated into absorption cross sections. These values are then used in atmospheric modeling simulations to determine the radiative forcing. Both kinetic and spectroscopic measurements have many potential experimental difficulties, which makes predicting global warming potentials (GWPs) from theory attractive. We build on our previous work from by examining an emerging class of compounds (fluorinated ethers) using theoretical chemistry to predict GWPs. Previous work investigated CH2F2 and found excellent comparison to experiment for predicting all intermediate steps for GWPs, including kinetic degradation rates with hydroxyl radical under low temperature tropospheric conditions, atmospheric lifetime estimates, radiative forcing in the atmospheric window, and overall GWPs at 20 year, 100 year, and 500 year time horizons. We find good agreement for all parameters for the hydrofluoroethers compared to experimental values. Radiative forcing estimates are also in good agreement with available experimental results. Finally, we now have a larger database of chemicals where we have verified our methodology of accurately predicting global warming potentials completely from theory.