Atmospheric Degradation Initiated by OH Radicals of the Potential Foam Expansion Agent, CF3(CF2)2CH═CH2 (HFC-1447fz): Kinetics and Formation of Gaseous Products and Secondary Organic Aerosols

The mechanism and kinetics of the atmospheric oxidation of CF3(CF2)2CHCH2 (HFC-1447fz) by hydroxyl radicals: ab initio investigation

The oxidation of 3,3,4,4,5,5,5-heptafluoro-1-pentene (HFC-1447fz) by hydroxyl radicals plays a crucial role in atmospheric conditions. By employing the CCSD(T)/cc-pVTZ//M06-2X/6-311++G(d,p) level of theory, the detailed reaction mechanism, kinetics and atmospheric implications of the degradation of HFC-1447fz by hydroxyl radicals were investigated. Compared to H-abstraction channels, the OH addition reaction is determined to be more favorable initial pathways in the degradation processes of HFC-1447fz. The overall rate coefficient of the degradation of HFC-1447fz by OH radicals is estimated to be 1.66 × 10-12 cm3 molecule-1 s-1 and the lifetime of HFC-1447fz is found to be 7 days at 298 K, which are in good agreement with the reported experimental results. The global warming potential (GWP) for HFC-1447fz on the 50, 100 and 500-year time horizons is estimated using the calculated rate coefficient. Furthermore, the mechanisms of the subsequent reactions of two OH-addition adducts have also been investigated. By TD-DFT calculations, it was found that eleven species can undergo photodissociation, while ten other species are photolytically stable under sunlight.

Diurnal photodegradation of fluorinated diketones (FDKs) by OH radicals using different atmospheric simulation chambers: Role of keto-enol tautomerization on reactivity

Rate coefficients for the gas-phase reactions of OH radicals with a series of fluorinated diketones have been determined for the first time at (298 ± 3) K and atmospheric pressure using the relative method and FTIR spectroscopy and GC-FID to monitor both reactants and references. The following values, in 10^-11 cm³ molecule^-1 s^-1, were obtained for 1,1,1-trifluoro-2,4-pentanedione (TFP), 1,1,1-trifluoro-2,4-hexanedione (TFH) and 1,1,1-trifluoro-5-methyl-2,4-hexanedione (TFMH), respectively: k₁(TFP + OH) = (1.3 ± 0.4), k₂(TFH + OH) = (2.2 ± 0.8), k₃(TFMH + OH) = (3.3 ± 1.0). The results are discussed with respect to the keto-enolic tautomerization specific for β-diketones. Based on the present results, the tropospheric lifetimes of TFP, TFH and TFMH upon degradation by OH radicals were calculated as 21, 13 and 8 h, respectively indicating that transport might play a role in the atmospheric fate of the studied compounds. Photochemical ozone creation potentials were estimated for TFP, TFH and TFMH to be: 23, 29 and 34, respectively.

FTIR product study of the Cl-initiated oxidation products of CFC replacements: (E/Z)-1,2,3,3,3-pentafluoropropene and hexafluoroisobutylene

A product study of the reactions of (E/Z)-1,2,3,3,3-pentafluoropropene ((E/Z)-CF3CF[double bond, length as m-dash]CHF) and hexafluoroisobutylene ((CF3)2C[double bond, length as m-dash]CH2) initiated by Cl atoms were developed at 298 ± 2 K and atmospheric pressure. The experiments were carried out in a 1080 L quartz-glass environmental chamber coupled via in situ FTIR spectroscopy to monitor the reactants and products. The main products observed and their yields were as follows: CF3C(O)F (106 ± 9)% with HC(O)F (100 ± 8)% as a co-product for (E/Z)-CF3CF[double bond, length as m-dash]CHF, and CF3C(O)CF3 (94 ± 5)% with HC(O)Cl (90 ± 7)% as a co-product for (CF3)2C[double bond, length as m-dash]CH2. Atmospheric implications of the end-product degradation are assessed in terms of their impact on ecosystems to help environmental policymakers consider HFOs as acceptable replacements.

First principle studies on the atmospheric oxidation of HFC-C1436 initiated by the OH radical

Study on the reactivity of HFC-C1436 with OH radical using electronic structure calculations.

Atmospheric fate of hydrofluoroolefins, CxF2x+1CHCH2 (x = 1,2,3,4 and 6): Kinetics with Cl atoms and products

Rate coefficients for the gas-phase reactions of C_xF_2x+1CHCH₂ (x = 1, 2, 3, 4 and 6) with Cl atoms were determined at (298 ± 2) K and (710 ± 5) Torr of air using a relative rate technique. Two experimental setups with simulation chambers were employed with Fourier Transform Infrared (FTIR) spectroscopy and Gas Chromatography coupled to Mass Spectrometry (GC-MS) as detection techniques. The Cl-rate coefficients obtained were (in 10^-10 cm³ molecule^-1 s^-1): (0.85 ± 0.11) for CF₃CHCH₂, (1.11 ± 0.08) for C₂F₅CHCH₂, (1.12 ± 0.18) for C₃F₇CHCH₂, (0.97 ± 0.09) for C₄F₉CHCH₂, and (0.99 ± 0.08) for C₆F₁₃CHCH₂. Additionally, the gas-phase products were identified and quantified, when possible, by FTIR spectroscopy or GC-MS. The main reaction product was reported to be C_xF_2x+1C(O)CH₂Cl. The fluorinated species, C_xF_2x+1CHO and C_xF_2x+1C(O)CH₂Cl, were identified. CF₃C(O)CH₂Cl and CF₃CHO were found to be formed with molar yield of (69 ± 5)% and (9 ± 1)%, respectively. The global lifetime of the investigated C_xF_2x+1CHCH₂ due to their Cl-reaction is more than 100 days so this route does not compete with the removal by OH radicals. This lifetime is long enough for C_xF_2x+1CHCH₂ to be transported to remote areas where they can be degraded. However, at a local scale, in marine regions at dawn the removal of C_xF_2x+1CHCH₂ is expected to occur in ca. 1 day. The atmospheric degradation of these hydrofluoroolefins by Cl atoms is not expected to be a source of bioaccumulative perfluorinated carboxylic acids, C_xF_2x+1C(O)OH. Additionally, the UV absorption cross sections of CF₃C(O)CH₂Cl were determined together with the rate coefficient of the OH reaction by an absolute kinetic method at room temperature.