High Precision Oxygen Isotope Ratio Measurements in Atmospherically Important Reactions and in Air Species

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The proposed research represents a continuation of isotopic measurements of atmospheric species and reactions of direct importance to tropospheric and stratospheric chemistry. The PI proposes to conduct five individual tasks: (1) Recent kinetic measurements by Troe et al. for O + O2 + M recombination have shown that, at pressures to 1,000 bar pressure, the rate constant varies in an unpredicted fashion which may be related to the anomalous 18O, 17O fractionation in O3 formation and in the stratosphere, which is presently not understood. High pressure, variable temperature, bath gas experiments are proposed to resolve the role of electronic excitation and radical complex mechanisms upon isotopic fractionation in O3 formation and to define the mechanism of the mass independent oxygen isotopic fractionation process in O3 formation. (2) Using presently developed experimental and theoretical techniques, the PI proposes to measure the rate of isotopic exchange between the species O3-O2-O and CO2,H2O, N2O and CO. Anomalously large 18O enrichments exist in stratospheric O3,H2O and CO2, but which are not understood. There are no measurements of most of the isotopic exchange rates needed to model these reactions. (3) The PI has found a new isotope effect in the thermal decomposition of O3. He proposes to resolve this mechanism as it is of importance to general isotopic fractionation processes and chemical reactions. (4) A variable 17O/18O ratio in atmospheric CO2 has been measured, which the PI has demonstrated is removed by CO2- H2O exchange. Determination of the source of the variable 17O/18O and exploration of applications as a quantitative measure of the lifetime of CO2-H2O exchange and general mixing, e.g. stratospheric-tropospheric exchange are planned (5) High precision 18O tropospheric O2 measurements will be maintained specifically to verify 18O variations in Santa Ana conditions and measure stratospheric O2 samples.