CF3CF=CH2 and (Z)-CF3CF=CHF: temperature dependent OH rate coefficients and global warming potentials

Area of Science:

• Atmospheric Chemistry
• Environmental Science
• Chemical Kinetics

Background:

• Hydrofluorocarbons (HFCs) are being phased out due to their high global warming potential.
• New HFCs are proposed as substitutes for HFC-134a in mobile air-conditioning units.
• Understanding the atmospheric reactivity of these substitutes is critical for environmental assessment.

Purpose of the Study:

• To determine the gas-phase reaction rate coefficients for OH radicals with 2,3,3,3-tetrafluoropropene (CF(3)CF=CH(2)) and (Z)-1,2,3,3,3-pentafluoropropene ((Z)-CF(3)CF=CHF).
• To evaluate the atmospheric lifetimes and global warming potentials of these potential HFC substitutes.

Main Methods:

• Pulsed-laser photolysis to generate OH radicals.
• Laser-induced fluorescence to detect OH radical concentrations.
• Measurements conducted under pseudo-first-order conditions over a temperature range of 206-380 K and pressures from 25 to 600 Torr.

Main Results:

• Rate coefficients for CF(3)CF=CH(2) are described by k(1)(T)=(1.26+/-0.11) x 10(-12) exp[(-35+/-10)/T] cm(3) molecule(-1) s(-1).
• Rate coefficients for (Z)-CF(3)CF=CHF are described by k(2)(T)=(1.6+/-0.2) x 10(-18)T(2) exp[(655+/-50)/T] cm(3) molecule(-1) s(-1), with an atmospheric-relevant Arrhenius expression k(2)(T)=(7.30+/-0.7) x 10(-13) exp[(165+/-20)/T] cm(3) molecule(-1) s(-1).
• Calculated global warming potentials are <4.4 for CF(3)CF=CH(2) and <3.6 for (Z)-CF(3)CF=CHF (100-year time horizon); atmospheric lifetimes are 12 and 10 days, respectively.

Conclusions:

• The measured reaction rates indicate short atmospheric lifetimes for both compounds.
• The low global warming potentials suggest these fluoropropenes are environmentally favorable alternatives to HFC-134a.
• The data are suitable for incorporation into atmospheric models to predict the environmental impact of these substances.