Isotopic enrichment of nitrous oxide (¹⁵N¹⁴NO, ¹⁴N¹⁵NO, ¹⁴N¹⁴N¹⁸O) in the stratosphere and in the laboratory

Nitrous oxide (N₂O) extracted from stratospheric whole air samples has been analyzed for its ¹⁵N and ¹⁸O isotopic composition, and strong enrichments in the heavy isotopes are observed concomitant with decreasing N₂O mixing ratio. Notably, the ¹⁵N enrichment is strongly different at the two nonequivalent positions in the molecule. Laboratory broadband photolysis experiments at wavelengths representative for the stratosphere confirm that photolysis is the prime cause for the observed fractionation in the stratosphere. However, the in situ stratospheric fractionation constants are significantly reduced compared to the laboratory data, reflecting the importance of dynamic processes. In addition, small but significant variations in the ratio of the two ¹⁵N fractionation constants indicate the influence of additional chemical processes like the oxidation of N₂O by O(¹D).