UV absorption cross sections of nitrous oxide (N₂O) and carbon tetrachloride (CCl₄) between 210 and 350 K and the atmospheric implications

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.