Role of Excited CF₃CFHO Radicals in the Atmospheric Chemistry of HFC-134a

Abstract

The atmospheric degradation of HFC-134a (CF3CFH2) proceeds via the formation of CF3CFHO radicals. Long path length FTIR environmental chamber techniques were used to study the atmospheric fate of CF3CFHO radicals. Two competing reaction pathways were identified for CF3CFHO radicals: reaction with O2, CF3CFHO + O2 → CF3C(O)F + HO2, and decomposition via C−C bond scission, CF3CFHO + M → CF3 + HC(O)F + M. CF3CFHO radicals were produced by two different reactions: either via the self-reaction of CF3CFHO2 radicals or via the CF3CFHO2 + NO reaction. It was found that decomposition was much more important when CF3CFHO radicals were produced via the CF3CFHO2 + NO reaction than when they were produced via the self-reaction of CF3CFHO2 radicals. We ascribe this observation to the formation of vibrationally excited CF3CFHO* radicals in the CF3CFHO2 + NO reaction. Rapid decomposition of CF3CFHO* radicals limits the formation of CF3C(O)F and hence CF3COOH in the atmospheric degradation of HFC-134a. We estimate that the CF3COOH yield from atmospheric oxidation of HFC-134a is 7−20%. Vibrationally excited alkoxy radicals may play an important role in the atmospheric chemistry of other organic compounds.

Rainwater trifluoroacetic acid (TFA) in Guangzhou, South China: Levels, wet deposition fluxes and source implication

“…c Kotamarthi et al, 1998). d (Wallington et al, 1996). e The reserve of fluoropolymers in China in the last 5 years was estimated to be 181,000 t (see Supporting Information).…”

“…Thus, it is important to acquire information about the fate and sources of TFA in the environment. Atmospheric degradation from HCFCs/HFCs has been regarded as an important source of environmental TFA due to globally large use and emission of these CFC-replacements (Wallington et al, 1994(Wallington et al, , 1996. HFC-134a, for example, as the most widely used HFCs in the world and also an important TFA precursor, was a cooling agent for mobile air conditioning systems (MACs) used in more than 80% of passenger cars and commercial vehicles worldwide (Velders et al, 2009).…”

Rate coefficients for the reactions of chlorine atoms with methanol and acetaldehyde

“…Mixtures containing Cl 2 and pairs of organics in air or N 2 were subjected to several consecutive irradiations and the ratio of the amount of each organic to that in the starting mixture was measured after each irradiation. 3 Pyrex cell through which the reactant gas mixtures flowed with a sufficient velocity to constantly replenish the gas mixtures without disturbing the kinetics. Chlorine atoms were produced by the 308 nm photolysis of Cl 2 using a pulsed XeCl excimer laser operated at 11 Hz giving a fluence of 10 -15 mJ cm Ϫ2 per pulse at the cell, which led to a fractional Cl 2 dissociation of (2 -3) ϫ 10 Ϫ3 .…”

“…The organic radicals produced are converted to peroxy radicals in air, and there is much interest in the atmospheric chemistry community in the reaction kinetics of these peroxy radicals. The reactions of Cl atoms with CH 3 OH and CH 3 and acetylperoxy (CH 3 COO 2 ) radicals, respectively [6 -10].…”

Ab Initio Study on the Thermal Decomposition of CH3CF2O Radical

“…The haloalkoxy radicals thus formed play an important role in the degradation mechanism of organic compounds in the troposphere. [12][13] There are two potentially accessible decomposition pathways that involve C-C bond scission and F-elimination as shown below:…”