Absorption cross sections of nitrous oxide (N2O) and carbon tetrachloride (CCl4) are reported at five atomic UV lines (184.95, 202.548, 206.200, 213.857, and 228.8 nm) at temperatures in the range 210–350 K. In addition, UV absorption spectra of CCl4 are reported between 200–235 nm as a function of temperature (225–350 K). The results from this work are critically compared with results from earlier studies. For N2O, the present results are in good agreement with the current JPL recommendation enabling a reduction in the estimated uncertainty in the N2O atmospheric photolysis rate. For CCl4, the present cross section results are systematically greater than the current recommendation at the reduced temperatures most relevant to stratospheric photolysis. The new cross sections result in a 5–7% increase in the modeled CCl4 photolysis loss, and a slight decrease in the stratospheric lifetime, from 51 to 50 years, for present day conditions. The corresponding changes in modeled inorganic chlorine and ozone in the stratosphere are quite small. A CCl4 cross section parameterization for use in atmospheric model calculations is presented
[1] The contribution of Halons, bromine-containing haloalkanes, to stratospheric ozone depletion is highly dependent on their atmospheric lifetime, which is primarily determined by UV photolysis. In this work, UV absorption cross-sections of the ozone-depleting substances CF 2 Br 2 (Halon-1202), CF 2 ClBr (Halon-1211), and CF 2 BrCF 2 Br (Halon-2402) were measured between 300 and 350 nm over the temperature range 210-296 K using cavity ringdown spectroscopy. Rayleigh scattering cross-sections were also determined and utilized in the cross-section determination. Spectra parameterizations are presented and 2-D atmospheric model calculations were used to determine global annually averaged atmospheric lifetimes of 2.52, 16.4, and 28.3 years, ozone depletion potentials (ODPs) of 1.95, 8.1, and 18.4, global warming potentials (GWPs) of 175, 1940, and 2270 (100-year time horizon), and associated uncertainties for CF 2 Br 2 , CF 2 ClBr, and CF 2 BrCF 2 Br, respectively. The revised lifetimes, ODPs, and GWPs differ from values currently reported in international assessments to evaluate ozone recovery and climate change. Citation: Papanastasiou,
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