Isotopic Composition of Nitrous Oxide and Carbon Dioxide

California Institute Of Technology, Pasadena CA

Investigators

Abstract

This project addresses the global budgets of nitrous oxide and carbon dioxide, which are two of the principal greenhouse gases in the terrestrial atmosphere. The project will involve modeling of microscopic molecular processes responsible for causing isotopic fractionation and atmospheric modeling, with emphasis on a quantitative evaluation of the mechanisms proposed for mass-independent fractionation and the interpretation of the recently discovered seasonal cycle of nitrous oxide. The research will focus on photolysis and kinetic rate coefficient computations, data analysis and atmospheric modeling of the principal isotopologues of the two target compounds, which have large and distinctive isotopic signatures driven primarily by fractionation processes in the middle atmosphere. An understanding of the multi-isotope fractionation patterns of atmospheric gases provides powerful constraints on their chemistry, transport and sources. A combination of the Caltech/JPL 2-dimensional and an isentropic version of the NCAR 3-dimensional MATCH (Model of Atmospheric Transport and Chemistry) will be used to explain the NOAA CMDL data, AGAGE (Advanced Global Atmospheric Gases Experiment) data, stratospheric data, and other available isotopic data. Additionally, inversion methods will be used to constrain the continental and oceanic sources of nitrous oxide. Another goal is to apply to carbon dioxide the same techniques that have recently been developed for nitrous oxide, to arrive at a fundamental understanding of the mechanisms for the isotopic fractionation and its dilution by transport processes. The isotopic fractionation of carbon dioxide may provide unique information on chemical and transport processes in the upper stratosphere and mesosphere, as well biospheric processes at the surface. A combination of the Caltech/JPL 2-dimensional and the NCAR 3-dimensional WACCM (Whole Atmosphere Community Climate Model) models will be used to model the isotopic composition of carbon dioxide from the surface to the mesosphere. The research efforts will contribute to the training of graduate students, postdoctoral fellows and undergraduates.