UV absorption cross sections of nitrous oxide (N2O) and carbon tetrachloride (CCl4) between 210 and 350 K and the atmospheric implications
1Earth System Research Laboratory, Chemical Sciences Division, National Oceanic and Atmospheric Administration, 325 Broadway, Boulder Colorado, 80305-3328, USA
2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder Colorado, 80309, USA
3NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
4Science Systems and Applications, Inc., Lanham, MD, 20706, USA
Abstract. 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.