Investigation into the Variability of the Stable Isotopic Composition of Tropospheric Nitrous Oxide

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The goal of the proposed research is to investigate the temporal evolution of the stable isotopic composition of atmospheric nitrous oxide in order to elucidate the global budget of this important greenhouse gas. Time series measurements will be made at four sites: La Jolla, CA; Clifton, NC; Trinidad Head, CA; and Cape Grim, Tasmania. Despite the long atmospheric lifetime of nitrous oxide (about 125 years), local concentration measurements show up to 3 percent excursions above baseline concentrations at La Jolla, CA and at Clifton, NC. Simultaneous measurements of other trace gases during periods of nitrogen oxide excursion point to an urban contribution at La Jolla and agricultural activity at Clifton. Measurements at these sites will be compared to those conducted at the two clear air sites in order to improve the global nitrous oxide budget. Separation and purification techniques have been developed for the isolation of pure N2O from air samples suitable for precise isotopic analysis by isotope ration mass spectrometry. Calibration and correction procedures have been developed to account for isobaric interferences caused by minute amounts of carbon dioxide, which are difficult to completely remove.