Isotopic Fractionation of Stratospheric Nitrous Oxide

Abstract

We propose an isotopic fractionation mechanism, based on photolytic destruction, to explain the 15 N/ 14 N and 18 O/ 16 O fractionation of stratospheric nitrous oxide (N 2 O) and reconcile laboratory experiments with atmospheric observations. The theory predicts that (i) the isotopomers 15 N 14 N 16 O and 14 N 15 N 16 O have very different isotopic fractionations in the stratosphere, and (ii) laboratory photolysis experiments conducted at 205 nanometers should better simulate the observed isotopic fractionation of stratospheric N 2 O. Modeling results indicate that there is no compelling reason to invoke a significant chemical source of N 2 O in the middle atmosphere and that individual N 2 O isotopomers might be useful tracers of stratospheric air parcel motion.