Atmospheric reaction of CH2=CHCH2OCF2CHF2 with OH radicals and Cl atoms, UV and IR absorption cross sections, and global warming potential.

Abstract

In this work, the rate coefficients for OH radical, k1(T), and Cl atom, k2(T), reaction with allyl 1,1,2,2-tetrafluoroethyl ether, CH2=CHCH2OCF2CHF2, were studied as a function of temperature and pressure in a collaborative effort made between UCLM, Spain, and LAPKIN, Greece. OH rate coefficients were determined in UCLM, between 263 and 353K and 50-600Torr, using the absolute rate method of pulsed laser photolysis-laser-induced fluorescence technique, while Cl kinetics were studied in temperature (260-363K) and pressure (34-721Torr) ranges, using the relative rate method of the thermostated photochemical reactor equipped with Fourier transform infrared spectroscopy as the detection technique. In both OH and Cl reactions, a negative temperature dependence of the measured rate coefficients was observed, which is consistent with complex association reactions. The temperature dependence of OH rate coefficients was found to be well represented by the following expression: k1(T) = (2.30 ± 0.35) × 10-12 exp[(544 ± 46) K/T] cm3 molecule-1s-1. In the case of the Cl-initiated reaction, a slight curvature was observed in the Arrhenius plot for k2(T), and the kinetic data were fitted to a modified Arrhenius expression: k2(T) = (4.42 ± 0.32) × 10-16 T2 exp[(610 ± 22) K/T] cm3 molecule-1s-1. No pressure dependence was observed in either case. These results are consistent with a complex reaction mechanism that is not uncommon in radical association reactions to the unsaturated bond. As part of this work, UV (200-400nm) and infrared absorption spectra (500-3200cm-1) were also measured to further evaluate CH2=CHCH2OCF2CHF2 atmospheric impact. Atmospheric lifetimes with respect to OH radical and Cl atom reactions were estimated to be 19.8h and 38days, respectively, showing that OH radicals dominate atmospheric oxidation. CH2=CHCH2OCF2CHF2 is a very weak absorber in the solar actinic region, while its relatively low radiative efficiency in the atmospheric IR window, 0.0034 W m-2 ppbv-1, and the short lifetime led to a very low GWP value relative to CO2, 1.2 × 10-2 and 3.3 × 10-3, at time horizons of 20 and 100years, respectively.