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1,1,1,3,3,‐pentafluorobutane (HFC‐365mfc): atmospheric degradation and contribution to radiative forcing
Author(s) -
Barry John,
Locke Garrett,
Scollard Donncha,
Sidebottom Howard,
Treacy Jack,
Clerbaux Cathy,
Colin Reginald,
Franklin James
Publication year - 1997
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1997)29:8<607::aid-kin6>3.0.co;2-y
Subject(s) - chemistry , reaction rate constant , troposphere , stratosphere , analytical chemistry (journal) , atmospheric pressure , hydrogen atom abstraction , molecule , atmosphere (unit) , photochemistry , hydrogen , thermodynamics , kinetics , meteorology , organic chemistry , quantum mechanics , physics
The rate constant for the reaction of the hydroxyl radical with 1,1,1,3,3‐pentafluorobutane (HFC‐365mfc) has been determined over the temperature range 278–323K using a relative rate technique. The results provide a value of k (OH+CF 3 CH 2 CF 2 CH 3 )=2.0×10 −12 exp(−1750±400/T) cm 3 molecule −1 s −1 based on k (OH+CH 3 CCl 3 )=1.8×10 −12 exp (−1550±150/T) cm 3 molecule −1 s −1 for the rate constant of the reference reaction. Assuming the major atmospheric removal process is via reaction with OH in the troposphere, the rate constant data from this work gives an estimate of 10.8 years for the tropospheric lifetime of HFC‐365mfc. The overall atmospheric lifetime obtained by taking into account a minor contribution from degradation in the stratosphere, is estimated to be 10.2 years. The rate constant for the reaction of Cl atoms with 1,1,1,3,3‐pentafluorobutane was also determined at 298±2 K using the relative rate method, k (Cl+CF 3 CH 2 CF 2 CH 3 )=(1.1±0.3)×10 −15 cm 3 molecule −1 s −1 . The chlorine initiated photooxidation of CF 3 CH 2 CF 2 CH 3 was investigated from 273–330 K and as a function of O 2 pressure at 1 atmosphere total pressure using Fourier transform infrared spectroscopy. Under all conditions the major carbon‐containing products were CF 2 O and CO 2 , with smaller amounts of CF 3 O 3 CF 3 . In order to ascertain the relative importance of hydrogen abstraction from the (SINGLE BOND)CH 2 (SINGLE BOND) and (SINGLE BOND)CH 3 groups in CF 3 CH 2 CF 2 CH 3 , rate constants for the reaction of OH radicals and Cl atoms with the structurally similar compounds CF 3 CH 2 CCl 2 F and CF 3 CH 2 CF 3 were also determined at 298 K k (OH+CF 3 CH 2 CCl 2 F)=(8±3)×10 −16 cm 3 molecule −1 s −1 ; k (OH+CF 3 CH 2 CF 3 )=(3.5±1.5)×10 −16 cm 3 molecule −1 s −1 ; k (Cl+CF 3 CH 2 CCl 2 F)=(3.5±1.5)×10 −17 cm 3 molecule −1 s −1 ]; k (Cl+CF 3 CH 2 CF 3 )<1×10 −17 cm 3 molecule −1 s −1 . The results indicate that the most probable site for H‐atom abstraction from CF 3 CH 2 CF 2 CH 3 is the methyl group and that the formation of carbonyl compounds containing more than a single carbon atom will be negligible under atmospheric conditions, carbonyl difluoride and carbon dioxide being the main degradation products. Finally, accurate infrared absorption cross‐sections have been measured for CF 3 CH 2 CF 2 CH 3 , and jointly used with the calculated overall atmospheric lifetime of 10.2 years, in the NCAR chemical‐radiative model, to determine the radiative forcing of climate by this CFC alternative. The steady‐state Halocarbon Global Warming Potential, relative to CFC‐11, is 0.17. The Global Warming Potentials relative to CO 2 are found to be 2210, 790, and 250, for integration time‐horizons of 20, 100, and 500 years, respectively. © 1997 John Wiley & Sons, Inc.