科研之友
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摘要
CF3CH=CH2 (hydrofluoroolefin, HFO-1243zf) is a potential replacement of high global-warming potential (GWP) hydrofluorocarbon (HFC-134a, CF3CFH2). Both the atmospheric lifetime and the radiative efficiency of HFO-1243zf are parameters needed for estimating the GWP of this species. Therefore, the aim of this work is (i) to estimate the atmospheric lifetime of HFO-1243zf from the reported OH rate coefficients, k(OH), determined under tropospheric conditions and (ii) to calculate its radiative efficiency from the reported IR absorption cross sections. The OH rate coefficient at 298 K also allows the estimation of the photochemical ozone creation potential (epsilon(POCP)). The pulsed laser photolysis coupled to a laser-induced fluorescence technique was used to determine k(OH) for the reaction of OH radicals with HFO-1243zf as a function of pressure (50-650 Torr of He) and temperature (263-358 K). Gas-phase IR spectra of HFO-1243zf were recorded at room temperature using a Fourier transform IR spectrometer between 500 and 4,000 cm(-1). At all temperatures, k(OH) did not depend on bath gas concentration (i. e., on the total pressure between 50 and 650 Torr of He). A slight but noticeable T dependence of k(OH) was observed in the temperature range investigated. The observed behavior is well described by the following Arrhenius expression: k(OH)(T)=(7.65 +/- 0.26) x10(-13) exp [(165 +/- 10)/T]cm(3) molecule(-1) s(-1). Negligible IR absorption of HFO-1243zf was observed at wavenumbers greater than 1,700 cm(-1). Therefore, IR absorption cross sections, sigma(v) over tilde, were determined in the 500-1,700 cm(-1) range. Integrated sigma(v) over tilde were determined between 650 and 1,800 cm-1 for comparison purposes. The main diurnal removal pathway for HFO-1243zf is the reaction with OH radicals, which accounts for 64 % of the overall loss by homogeneous reactions at 298 K. Globally, the lifetime due to OH reaction (tau(OH)) was estimated to be 8.7 days under the assumption of a well-mixed atmosphere. Assuming other removal pathways, the atmospheric lifetime (tau) was estimated to be similar to 6 days. Considering the estimated tau(OH) and the measured IR absorption cross sections of HFO-1243zf in the atmospheric window (720-1,250 cm(-1)), its lifetime corrected radiative efficiency was calculated to be 0.019 W m(-2) ppbv(-1). GWP(100 years) for the HFO investigated, 0.29, is negligible compared to that of HFC-134a, the HFC to be potentially replaced (GWP(100 years) = 1,300, Hodnebrog et al. (Rev Geophys 51: 300-378, 2013)). epsilon(POCP) for HFO-1243zf was estimated to be around 1 order of magnitude lower than that for ethylene. In conclusion, HFO-1243zf is fast degraded in the atmosphere, and it does not appreciably contribute to global warming and local/regional air pollution. Therefore, HFO-1243zf can be a suitable replacement for HFC-134a in air conditioning units.
- 出版日期2015-4
