The environmental impact of unsaturated fluoroesters: atmospheric chemistry towards OH radicals and Cl atoms, radiative behavior and cumulative ozone creation

Abstract

Smog chamber/GC techniques were used to investigate the atmospheric degradation of two hydrofluoroesters (allyl trifluoroacetate (CF₃C(O)OCH₂CHCH₂) and vinyl trifluoroacetate (CF₃C(O)OCHCH₂)) by oxidation with OH radicals and Cl atoms at 298 K and an atmospheric pressure of N₂ or air. The measured rate coefficients were (in units of cm³ per molecule per s): k_{allyl trifluoroacetate+OH} = (9.27 ± 3.81) × 10⁻¹²; k_{vinyl trifluoroacetate+OH} = (8.07 ± 1.92) × 10⁻¹²; k_{allyl trifluoroacetate+Cl} = (1.75 ± 0.21) × 10⁻¹⁰ and k_{vinyl trifluoroacetate+Cl} = (2.08 ± 0.16) × 10⁻¹⁰. In the OH-initiated oxidation of allyl trifluoroacetate, the identified product can arise from OH addition to both carbons in the double bond and the later decomposition of the alkoxy radical formed. However, in the reactions of both fluoroesters with Cl atoms, the main product detected arises from Cl addition to the terminal carbon atom and the subsequent reaction of the chloroalkoxy radical formed with O₂. Infrared spectra of the studied esters were collected and their contribution to global warming was assessed by calculating their radiative efficiencies. Combining these results with the kinetic data we found that their global warming potentials are negligible. Finally, the photochemical ozone creation potentials were calculated, obtaining values lower than those of non-fluorinated unsaturated hydrocarbons.