Stratospheric N 2 O is known to be enriched in the heavy isotopes 15 N and 18 O relative to tropospheric N 2 O, primarily because of the preferential photolysis of light isotopologues. We present measurements of δ 15 N, δ 18 O, and site‐specific δ 15 N on N 2 O from 32 stratospheric whole air samples collected by the NASA ER‐2 aircraft between 1997 and 2000 from 62°N to 89°N with N 2 O mixing ratios ranging from 51 to 313 ppbv. The relationships between the isotopic compositions and N 2 O mixing ratios show significant differences between aircraft deployments and with previous measurements for N 2 O < 200 ppbv. The differences between ER‐2 deployments at low N 2 O are significant at the 3σ level and are due to the effects of transport and mixing. The ratios of enrichment factors for the different isotopologues, however, are the same to within their 1σ uncertainties for N 2 O > 200 ppbv and N 2 O < 200 ppbv. The observed isotope:N 2 O relationships are also used to estimate the fluxes of the N 2 O isotopologues from the stratosphere to the troposphere given independent estimates of the N 2 O loss rate. On the basis of the robustness of isotope:N 2 O relationships for N 2 O > 200 ppbv we conclude that the fluxes to the troposphere estimated from these relationships and, therefore, the influence of stratosphere‐to‐troposphere transport on the isotopic compositions of N 2 O in the free troposphere are now relatively well quantified, leaving the isotopic compositions of the N 2 O sources as the remaining largest uncertainties in the global N 2 O isotope budget.
No takes yet. Share an insight, caveat, or question.
Park et al. (2004) studied this question.