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_2O) 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_2O. Modeling results indicate that there is no compelling reason to invoke a significant chemical source of N_2O in the middle atmosphere and that individual N_2O isotopomers might be useful tracers of stratospheric air parcel motion.