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Nitrous oxide
N2O is both an important greenhouse gas and is involved in stratospheric ozone destruction. Source rates at the surface are small relative to its total abundance and its major sink is photolysis in the stratosphere. The currently large uncertainties in accounting for indivdual sources can be additionally constrained by isotopic maesurements. The main sink of N2O is photolysis in the stratosphere with a marked asymmetry between different isotopomers of N2O (Yung and Miller, 1997).
Recent analysis of balloon borne FTIR observations by one of us
(Griffith et al., 2000) show a strong enrichment for stratospheric
14N15N16O quantitatively consistent with the ground-based data we present
here and with laboratory spectroscopy (Turatti et al., 2000).
To our knowledge the observations reported here are the first
attempt made by remote sensing from ground. N2O is still work in progress. Currently we can only show a scatter
plot of total columns of 14N15N16O versus 14N14N16O from indivdual observations. The line parameters used are the
most recent ones published by Toth et al (2000 and references
therein). However, we are confident to present shortly altitude
resolved data and to provide two more isotopomers.
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Figure 3: This scatter plot illustrates the enrichment of 14N15N16O to the bulk species 14N14N16O (456/446 N2O) relative to the isotopic enrichment assumed in the R.Toth spectroscopic data (Toth, 2000). At this stage our data is to be seen as a feasability study. Not all potential sources of systematic error have been fully adressed. However, we are confident that the enrichment shown for 14N15N16O is in any case significant, though there is still some uncertainty on the absolute scale. We have also identified suitable absortption lines to quantify 15N14N16O and 14N14N18O, but no time was left to prepare that data adequately for this conference. Please note also that we used profiling in our analysis and aim to present altitude resolved isotopic data.
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