Stable isotope fractionation during ultraviolet photolysis of N2O

biogeochemical cycling of nitrous oxide plays an important role in greenhou se forcing and ozone regulation. Laboratory studies of N2O:N-2 mixtures irr adiated between 193-207 nm reveal a significant enrichment of the residual heavy nitrous oxide isotopomers. The isotopic signatures resulting from pho tolysis are well modeled by an irreversible Rayleigh distillation process, with large enrichment factors of epsilon(15,18)(193 nm)= -18.4, -14.5 per m il and epsilon(15,18)(207 nm)= -48.7, - 46.0 per mil. These results, when c ombined with diffusive mixing processes, have the potential to explain the stratospheric enrichments previously observed.