Ole John Nielsen

Photochemical reactors were used to study the Cl-atom- and OH-radical-initiated oxidation of several oxygenates, including the title compound, 3,3,3-trifluoropropane-1,2-diol (CF3CH(OH)CH2OH), in 700 Torr of air or N2 diluent at 296 K. Using relative rate methods, k(Cl + CF3CH(OH)CH2OH) = (6.8 ± 1.3) × 10–12 cm3 molecule–1 s–1 and k(OH + CF3CH(OH)CH2OH) = (1.6 ± 0.3) × 10–12 cm3 molecule–1 s–1 were determined. The atmospheric lifetime with respect to reaction with OH radicals is estimated at 7.2 days for CF3CH(OH)CH2OH. The primary oxidation products were identified as α-hydroxy carbonyls with absorption bands located at 1753 and 1780 cm–1, assigned to the formation of CF3CH(OH)CHO and CF3C(O)CH2OH, respectively. Nonlinear fits were used to estimate k(Cl + CF3CH(OH)CHO) = (4 ± 1) × 10–12 cm3 molecule–1 s–1 and k(Cl + CF3C(O)CH2OH) = (9 ± 4) × 10–13 cm3 molecule–1 s–1. Major final products are CF3CHO, CF3C(O)OH, and COF2. As part of this study, the IR spectrum of CF3C(O)CHO was recorded and the rate coefficient k(Cl + CF3C(O)CHO) = (9.7 ± 1.0) × 10–13 cm3 molecule–1 s–1 was determined. The products and the oxidation mechanism are discussed in the context of the atmospheric degradation of third-generation CFC-replacement compounds.

Photolysis of CF ₃ CH(OH)CH ₂ Br in air at 254 nm generates CF ₃ CH(OH)CHO, a possible degradation product from the atmospheric oxidation of HFO-1336mzz (CF ₃ CHCHCF ₃ ).

Smog chamber investigation of the Cl atom and OH radical reactions with CF ₃ CH(OH)CH(OH)CF ₃ and the photolysis of CF ₃ C(O)C(O)CF ₃ . Results are discussed in the context of the atmospheric degradation of 3rd gen. CFC-replacement compounds.

2‐chloro‐3,3,3‐trifluoropropene, CF ₃ C(Cl)═CH ₂ (HCFO‐1233xf), is a volatile hydrochlorofluoroolefin, commonly used in industrial synthesis of other halogenated olefins. Kinetics and reaction mechanisms for the reactions of OH radicals, Cl atoms, and O ₃ with CF ₃ C(Cl)═CH ₂ were investigated using FTIR/smog chamber studies in 700 Torr of air/N ₂ diluent at 295 ± 2 K. The rate constants k (Cl + CF ₃ C(Cl)═CH ₂ ) = (8.3 ± 1.1) × 10 ⁻¹¹ , k (OH + CF ₃ C(Cl)═CH ₂ ) = (3.4 ± 0.8) × 10 ⁻¹² and k (O ₃ + CF ₃ C(Cl)═CH ₂ ) = (2.5 ± 0.1) × 10 ⁻²¹ cm ³ molecule ⁻¹ s ⁻¹ , were measured. An atmospheric lifetime of 3.3 days for CF ₃ C(Cl)═CH ₂ was determined, dominated by reaction with OH radicals. The reaction of OH radicals and Cl atoms with CF ₃ C(Cl)═CH ₂ proceeds by addition to the double bond, and primary and secondary products of the reactions were quantified. Approximately 90% of Cl atoms undergo addition to the terminal carbon. We were unable to establish any preference of reaction site of the OH addition. Reaction of O ₃ with CF ₃ C(Cl)═CH ₂ leads to the formation of Criegee intermediates that decompose yielding CF ₃ C(O)Cl and HC(O)H as major products. An upper limit of < 0.3% for the yield CF ₃ Cl was estimated. The integrated IR absorption cross‐section for CF ₃ C(Cl)═CH ₂ is (1.22 ± 0.06) × 10 ⁻¹⁶ cm molecule ⁻¹ (600–1800 cm ⁻¹ ). The effective radiative efficiency was determined as 0.007 W m ⁻² ppb ⁻¹ leading to a Global Warming Potential (GWP) for the 100‐year time horizon of 0.031. The environmental impact of release of CF ₃ C(Cl)═CH ₂ to the atmosphere is discussed.

2-Fluorobutane (HFC-3-10-1se, CH₃CHFCH₂CH₃), a simple fluoroalkane, has received less attention than other widely used hydrofluorocarbons. Understanding its atmospheric chemistry is essential for evaluating its potential as a low- Global Warming Potential (GWP) alternative in industrial applications. Currently, only estimates of GWP relative to carbon dioxide (CO₂) at time horizons of 20 and 100 years (GWP₂₀ and GWP₁₀₀) have been reported to be 4 and 1, respectively, based on the calculated radiative efficiency (RE) and estimated rate coefficients (k _OH) for the gas-phase reaction of hydroxyl (OH) radicals. Here, we present the first experimental kinetic study of the gas-phase reaction of OH radicals with CH₃CHFCH₂CH₃ using a pulsed laser photolysis/laser-induced fluorescence technique (PLP-LIF) (T = 264.0–353.2 K; P = 60–230 Torr of helium). Contrary to previous estimates, no temperature dependence of the OH-rate coefficients, k _OH(T), was observed. A weighted average of k _OH(T)=(1.75 ± 0.56)×10^–12 cm³ molecule^–1 s^–1 corresponds to a global tropospheric lifetime, τ_OH, of 6.7 days. Additionally, the ultraviolet (UV, λ = 190–300 nm) and infrared (IR, 3500–500 cm^–1) absorption cross sections of CH₃CHFCH₂CH₃ were determined at 298 K by gas-phase UV and Fourier Transform infrared (FTIR) spectroscopies. No absorption above 219 nm was observed, therefore UV photolysis of 2-fluorobutane in the solar actinic region (λ > 290 nm) is not expected. From the IR absorption cross sections, the instantaneous radiative efficiency (RE_inst) was calculated to be 0.0562 W m^–2 ppbv^–1, while RE with atmospheric lifetime correction and adjustment for stratospheric temperature was 0.0037 W m^–2 ppbv^–1. Using lifetime corrected RE and τ_OH values, GWP₂₀ and GWP₁₀₀ were calculated to be 0.220 and 0.062. These findings suggest that its rapid atmospheric removal minimizes its contribution to climate change.

The atmospheric chemistry of 1,4‐difluorobutane (CFH ₂ CH ₂ CH ₂ CFH ₂ ) was investigated through a kinetic and mechanistic study of the reaction with chlorine (Cl) atoms and hydroxyl (OH) radicals. Using Fourier transform infrared (FTIR) spectroscopy and relative rate methods, the rate constants ( k ) for the reactions were determined at 298 ± 2 K as k (Cl + CFH ₂ CH ₂ CH ₂ CFH ₂ ) = (2.96 ± 0.31) × 10 ⁻¹¹ cm ³ molecule ⁻¹ s ⁻¹ and k (OH + CFH ₂ CH ₂ CH ₂ CFH ₂ ) = (8.23 ± 0.77) × 10 ⁻¹³ cm ³ molecule ⁻¹ s ⁻¹ . The major product formed in both reactions was HC(O)F. Additional primary and secondary products were observed, and a proposed degradation mechanism is presented. The atmospheric lifetime of 1,4‐difluorobutane with respect to reaction with OH radicals was determined to be 29 days. The IR spectrum of 1,4‐difluorobutane was obtained using FTIR at Copenhagen Center for Atmospheric Research (CCAR) and at University of Castilla–La Mancha (UCLM). From these measurements, the radiative efficiency of CFH ₂ CH ₂ CH ₂ CFH ₂ was calculated resulting in a lifetime‐adjusted effective radiative efficiency of 0.015 W m ⁻² ppb ⁻¹ . The Global Warming Potential (GWP) values for CFH ₂ CH ₂ CH ₂ CFH ₂ were determined to 3.1, 0.9, and 0.3 for time horizons of 20, 100, and 500 years, respectively.

The UV-B (broadband 280–320 nm, peak λ = 313 nm) and UV-C (λ = 254 nm) initiated photolytic oxidation of 1,1-difluoroacetone (CF₂HC(O)CH₃) and 1,1,1-trifluoroacetone (CF₃C(O)CH₃) was studied as a function of total pressure using smog chamber techniques. The UV spectrum of CF₂HC(O)CH₃ and CF₃C(O)CH₃ are reported; the former for the first time. The UV-B and UV-C photolysis rates were measured relative to that of CH₃C(O)CH₃. The approximate UV-B (313 nm) quantum yield for CF₂HC(O)CH₃ and CF₃C(O)CH₃ were determined as 0.03 and 0.007. At 254 nm, the overall quantum yields for CF₂HC(O)CH₃ and CF₃C(O)CH₃ were determined as (1.11 ± 0.13) and (0.69 ± 0.08), respectively, at 700 Torr, (298 ± 1) K, independent of diluent gas. This is the first chamber study of the photolysis of CF₂HC(O)CH₃ and CF₃C(O)CH₃. The measured yields of HCOF, COF₂ (and CO) suggest that photolysis of CF₂HC(O)CH₃ and CF₃C(O)CH₃ produces CF₂H and CF₃ radicals, respectively, both in yields of unity. Additional products identified include CH₃OH and HCHO. Pressure-dependent decomposition pathways were identified in the UV-C photolysis and overall photolysis mechanisms are proposed. Finally, the atmospheric photolysis-lifetimes of CF₂HC(O)CH₃ and CF₃C(O)CH₃ were estimated based on a Tropospheric Ultraviolet Visible (TUV) model calculation.

We comment on the recent article by Vincent at al.

HFO-1132E (( E )-1,2-difluoroethene) has an estimated atmospheric lifetime on the order of 1 day, atmospheric degradation gives HC(O)F as the sole product and the global warming potential (100 years) of HFO-1132E is ≪1.