A computer-based solution to the oxidation kinetics of fluorinated and oxygenated volatile organic compounds

Abstract

The OH radical is the most powerful atmospheric oxidant, being responsible for the chemical breakdown of many pollutants released into the troposphere, including saturated volatile organic compounds (VOCs). Numerous of these VOCs are strong greenhouse gases, including hydrofluorocarbons, whose industrial emissions to the environment have grown significantly over time and are gradually being phased out. The calculation of OH-initiated oxidation reaction rate constants represents an approach to determine the atmospheric impact of fluorine-containing oxygenated VOCs, which have been regarded as a good substitute for hydrofluorocarbons. Such calculations are challenging, especially when the VOCs are conformationally flexible. We have recently developed a cost-effective computational protocol for such systems based on density functional calculations and on the coupling of multiconformer transition state theory with constrained transition state randomization. The protocol has, however, only been calibrated against a small number of experiments, practically all of which involved OVOCs from the ether family. In this study, we extend the scope by applying the protocol to five families of OVOCs (C3-fluorine containing alcohols, aldehydes, esters, ethers and ketones) and compare the calculated reaction rates with the recommended experimental values. Our calculated rate coefficients, on average, agree with the recommended experimental values to within a factor of two, with the maximum deviation being a factor of 2.8. These results validate the use of the protocol for computational tropospheric degradation studies of conformationally flexible OVOCs with an unprecedented accuracy.