Atmospheric Chemistry of CF_3OCF_2CF_2H and CF_3OC(CF_3)_2H:Reaction with Cl Atoms and OH Radicals,Degradation Mechanism,Global Warming Potentials,and Empirical Relationship between k(OH)and k(Cl)for Organic Compounds

摘要

Using FTIR smog chamber techniques,k(Cl + CF_3OCF_2CF_2H)=(2.70(+-)0.52)x 10~(-16),k(OH + CF_3OCF_2-CF_2H)=(2.26(+-)0.18)x 10~(-15),k(Cl + CF_3OC(CF_3)_2H)=(1.58(+-)0.27)x 10~(-18)and k(OH + CF_3OC-(CF_3)_2H)=(3.26(+-)0.95)x 10~(-16)cm~3 molecule~(-1)s~(-1)were measured.The atmospheric lifetimes of CF_3OCF_2CF_2H and CF_3OC(CF_3)_2H are estimated to be 27 and 216 years,respectively.Chlorine atom initiated oxidation of CF_3OCF_2CF_2H in 700 Torr of air in the presence of NO_x gives CF_3OC(O)F in a molar yield of 36(+-)5% and COF_2 in a molar yield of 174(+-)9%,whereas oxidation of CF_3OC(CF_3)_2H gives CF_3OC(O)CF_3 and COF_2 in molar yields that are indistinguishable from 100%.Quantitative infrared spectra were recorded and used to estimate global warming potentials of 3690 and 8230(100 year time horizon,relative to CO_2)for CF_3OCF_2CF_2H and CF_3OC(CF_3)_2H,respectively.All experiments were performed in 700 Torr of N_2/O_2 diluent at 296(+-)2 K.An empirical relationship can be used to estimate the preexponential factor,which can be combined with k(298 K)to give the temperature dependence of reactions of OH radicals with organic compounds proceeding via H-atom abstraction:log(A)=(0.239(+-)0.027)log(k(OH))-(8.69(+-)0.372),k(OH)is the rate constant at 298 K and n is the number of H atoms.The rates of H-atom abstraction by OH radicals and Cl atoms at 298 K from organic compounds are related by the expression log(k(OH))=(0.412(+-)0.049)log(k(Cl))-(8.16(+-)0.72).The utility of these expressions and the atmospheric chemistry of the title hydrofluoroethers are discussed.