Cross-sections and quantum yields for the atmospheric photolysis of the potent greenhouse gas nitrogen trifluoride

Although NF3, a trace gas of purely anthropogenic origin with a large global warming potential is accumulating in the Earth's atmosphere, little photochemical data exists from which to calculate its atmospheric removal rate. In this study, photodissociation quantum yields, Φ1, were derived following 193.3 nm laser photolysis of NF3, and quantitative conversion of the F-atom photoproducts to OH, which was detected by laser induced fluorescence. Values of Φ1(P, T) = (1.03 ± 0.05) were determined at pressures between 28 and 100 mBar of He or N2 and at either room temperature or 255 K. Absorption cross-sections, σ, obtained between 184 and 226 nm were combined with the values of Φ1(P, T) to confirm a long (≈700 year) photolysis lifetime for NF3. No evidence for reaction of OH with NF3 was found, indicating that this process makes little or no contribution to NF3 removal from the atmosphere. These results underpin recent calculations of an NF3 atmospheric lifetime τ ≈ 550 years, largely controlled by photolysis in the stratosphere. In the course of this work the rate coefficient k2(298 K) = (1.3 ± 0.2) × 10−11 cm3 molecule−1 s−1 was obtained for the reaction F + H2O.