Rate constants for the gas-phase reactions of (Z)-CF3CH CHF and (E)-CF3CH CHF with OH radicals at 253–328 K

A Computational Perspective on the Chemical Reaction of HFO-1234zc with the OH Radical in the Gas Phase and in the Presence of Mineral Dust

The gas phase and heterogeneous reaction on mineral dust aerosols of trace gases could significantly affect the tropospheric oxidation capacity and aerosol composition of the atmosphere. In this work, the OH radical-initiated oxidation of a hydrofluoroolefin, HFO-1234zc, and subsequent reaction of favorable intermediates with other reactive species, such as O₂, HO₂, and NO_x (x = 1-2) radicals, were studied, and the role of mineral dust in the form of silicate clusters on the reaction mechanism and rate constant was studied. In the gas phase, OH radical addition to HFO-1234zc is kinetically more favorable than the H-atom abstraction reaction. The calculated reaction energy barrier and thermochemical parameters show that both the initial reactions are more feasible on silicate clusters. Thus, silicates can act as chemical sinks for trapping of hydrofluoroolefins (HFOs). It is found that both gas-phase and heterogeneous reactions are responsible for the transformation of HFOs into fluorinated compounds in the atmosphere. Further, the results show that the ozone creation potential of HFO-1234zc is low, and few of the products are harmful to aquatic organisms. This study provides new insights on the formation of toxic pollutants from the oxidation of HFO-1234zc, which may have significant implications in the troposphere.

Trends of Studies on Controlled Halogenated Gases under International Conventions during 1999–2018 Using Bibliometric Analysis: A Global Perspective

A lot of research on international convention-controlled halogenated gases (CHGs) has been carried out. However, few bibliometric analyses and literature reviews exist in this field. Based on 734 articles extracted from the Science Citation Index (SCI) Expanded database of the Web of Science, we provided the visualisation for the performance of contributors and trends in research content by using VOSviewer and Science of Science (Sci2). The results showed that the United States was the most productive country, followed by the United Kingdom and China. The National Oceanic and Atmospheric Administration had the largest number of publications, followed by the Massachusetts Institute of Technology (MIT) and the University of Bristol. In terms of disciplines, environmental science and meteorological and atmospheric science have contributed the most. By using cluster analysis of all keywords, four key research topics of CHGs were identified and reviewed: (1) emissions calculation, (2) physicochemical analysis of halocarbons, (3) evaluation of replacements, and (4) environmental impact. The change in research substances is closely related to the phase-out schedule of the Montreal Protocol. In terms of environmental impact, global warming has always been the most important research hotspot, whereas research on ozone-depleting substances and biological toxicity shows a gradually rising trend.

Theoretical study on the reaction mechanism of OH radical with Z(E)-CF3CHCHF

The comprehensive transformation mechanism and kinetics of Z(E)-CF₃CHCHF initiated by OH radicals were investigated by performing quantum chemical calculations.

Rate constants for the reactions of OH radicals with CF3CX=CY2 (X = H, F, CF3, Y = H, F, Cl)

The rate constants of OH radicals with CF₃CF=CCl₂, CF₃CH=CF₂, CF₃CF=CH₂, CF₃CH=CH₂, and (CF₃)₂C=CH₂ have been measured over the temperature range 250-430 K. Kinetic measurements have been carried out using flash photolysis and laser photolysis methods combined respectively with laser-induced fluorescence technique. The Arrhenius rate parameters have been determined as k(CF₃CF=CCl₂) = (6.50 ± 0.22) × 10^-13∙exp[(200 ± 10)/T], k(CF₃CH=CF₂) = (4.85 ± 0.14) × 10^-13∙exp[(120 ± 10)/T], k(CF₃CF=CH₂) = (1.54 ± 0.03) × 10^-12∙exp[- (100 ± 10)/T], k(CF₃CH=CH₂) = (1.06 ± 0.02) × 10^-12∙exp[(80 ± 10)/T], and k((CF₃)₂C=CH₂) = (8.75 ± 0.23) × 10^-13∙exp[- (20 ± 10)/T] cm³ molecule^-1 s^-1. Infrared absorption spectra of the halogenated alkenes have been measured at room temperature. The atmospheric lifetime, global warming potential, ozone depleting potential, and photochemical ozone creation potential have been estimated. The change in the reactivity of halogenated alkenes by the substitution has been examined by considering the structure containing the atoms or atomic groups attached to the carbons on both sides of the double bond.