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

大气重要反应和空气物种中的高精度氧同位素比测量

• 批准号: 9020462
• 负责人: Mark Thiemens
• 金额: $ 47.47万
• 依托单位: University of California-San Diego
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1991
• 资助国家: 美国
• 起止时间: 1991-03-15 至 1995-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9020462&HistoricalAwards=false
• 关键词: Precision; Oxygen; Isotope; Ratio; Measurements

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.

拟议的研究是对大气物质和对对流层和平流层化学具有直接重要性的反应进行同位素测量的继续。PI计划进行五项单独的任务：(1)Troe等人最近对O + O2 + M复合的动力学测量表明，在压力达到1,000 bar的压力下，速率常数以一种不可预测的方式变化，这可能与O3地层和平流层中异常的18O、17O分馏有关，这一点目前尚不清楚。提出了高压、变温、浴气实验，以解决电子激发和自由基复杂机制对O3形成过程中同位素分馏的作用，并确定O3形成过程中不依赖质量的氧同位素分馏过程的机理。(2)利用目前发展的实验和理论技术，PI提出测量O3- o2 - o与CO2、H2O、N2O和CO之间的同位素交换速率。平流层O3、H2O和CO2中存在异常大的18O富集，但尚未了解。对这些反应建立模型所需的大多数同位素交换率都没有测量。(3) PI在O3热分解过程中发现了新的同位素效应。他建议解决这一机制，因为它对一般同位素分馏过程和化学反应具有重要意义。(4)测量了大气中17O/18O比值的变化，PI已证明该变化可通过CO2- H2O交换消除。计划确定变量17O/18O的来源，并探索作为CO2-H2O交换和一般混合寿命的定量测量的应用，例如平流层-对流层交换。(5)将保持高精度的18O对流层O2测量，专门用于验证Santa Ana条件下的18O变化并测量平流层O2样品。