Photolysis of CF3CHO at 254 nm and potential contribution to the atmospheric abundance of HFC-23

In this work, the 254 nm photolysis of CF3CHO was investigated using a 101 L quartz chamber coupled with FTIR detection. The overall quantum yield was determined as (0.52 +/- 0.07) at 700 Torr, independent of diluent gas. Photolysis in 700 Torr N2 and in the presence of NO yields (26 +/- 3) % CF3H and (73 +/- 6) % CF3NO. In 700 Torr of air or oxygen, products identified include CF3H, COF2, CF3OH, CF3O2CF3 and CF3O3CF3. In the presence of NO in 700 Torr of air or O2, alkoxy-and peroxy-nitrates were also quantified. A full carbon balance for the fluorine -bearing carbon was achieved. The photolytic channel quantum yields were established: phi(CF3H + CO) = (0.16 +/- 0.02) and phi(CF3 + HCO) = (0.36 +/- 0.07) at 700 Torr total pressure. This is the first large chamber study of the stratospheric photolysis of CF3CHO. The quantum yields measured here are lower than those reported previously and show a different relative importance associated with the photolysis channels. Atmospheric photolysis coefficients of CF3CHO were modeled giving an estimate for the average atmospheric lifetime for CF3CHO of 13 +/- 4 days (at 5 km altitude, tropics). Based on the present work, photolytic production of CF3H, which is a strong greenhouse gas, can occur at stratospheric altitudes above 30-40 km. This has implications for the environmental impact of CF3CHO generated as an oxidation product in the higher atmosphere from long-lived chlorofluoro-carbon-replacement compounds. However, the majority of CF3CHO will undergo photochemical degradation in the lower troposphere. Hence, photochemical degradation of CF3CHO will make a negligible contribution to the atmospheric burden of CF3H.