Measurements of hydrogen isotope ratios in atmospheric volatile organic compounds

通过测量大气挥发性有机化合物(VOC)在环境浓度下的稳定同位素比率，可以调查这些化合物的来源、光化学历史、停留时间和大气收支。然而，到目前为止，所有关于环境VOC的研究都集中在碳同位素比率上。原则上，对其他元素的同位素比值的研究可以进一步提高我们对大气过程的理解。氢的稳定同位素比率的测量将特别有希望。由于氢同位素的质量比大于碳同位素的质量比，氢同位素效应将比碳同位素效应更为明显。我们提出用气相色谱热解同位素比质谱仪(GC-P-IRMS)测量大气中挥发性有机物的稳定氢同位素比值。在现有大气挥发性有机碳稳定碳同位素比值测定方法的基础上，提出了一种大气挥发性有机碳氢同位素比值的测定方法。为了满足必要的重现性和检测限，需要高容量的空气样品(取决于挥发性有机化合物浓度高达200 L)，以提供足够量的挥发性有机化合物。因此，我们对现有的预浓缩系统进行了相应的修改。与此同时，我们彻底描述了该系统的特点。我们可以证明，该系统非常适合于测量由于大气中的化学和物理过程而引起的环境VOC中氢同位素比率的变化。对环境空气中VOC的首次测量产生了令人振奋的结果。根据迄今的经验，我们计划改进预富集系统，以进一步减少空气样品中的水和二氧化碳，并测试新的吸附剂，以提高预浓集和增加可测量化合物的光谱。同时，还将测量缺失的动力学同位素效应以及排放源挥发性有机化合物中的同位素比率。在这些调查之后，将进行更长期的测量，以调查日变化和季节变化。此外，还将开发新的工具来解释和应用数据。该方法是确定VOC的来源、研究其大气过程、区分混合和化学过程对其分布的影响以及化合物的停留时间的灵敏工具。据我们所知，到目前为止，还没有关于大气VOC中稳定氢同位素比值的测量报告。新类型的测量将增加另一条重要信息，以更好地了解大气中的化学和物理过程。

Measurements of stable isotope ratios in atmospheric volatile organic compounds (VOC) at ambient concentrations allow investigating sources, photochemical history, residence times, and atmospheric budgets of these compounds. However, up to now all studies concerning ambient VOC concentrated on carbon isotope ratios. In principle, the investigation of isotope ratios of other elements can further improve our understanding of atmospheric processes. Measurements of stable isotope ratios of hysdrogen would be especially promising. Hydrogen isotope effects will be more pronounced than carbon isotope effects because the mass ratio of hydrogen isotopes is larger than that of carbon isotopes. We propose to measure stable hydrogen isotope ratios of volatile organic compounds in the atmosphere using a gas chromatograph pyrolysis isotope ratio mass spectrometer (GC-P-IRMS). We developed a method for measurements of hydrogen isotope ratios of atmospheric VOC based on a modification of existing methods for the measurement of stable carbon isotope ratios in atmospheric VOC. To meet the necessary reproducibility and detection limits, high volume air samples are needed (depending on the VOC concentrations up to 200 L) to supply a sufficient amount of VOC. Therefore, we modified the existing preconcentration system accordingly. Meanwhile, we thoroughly characterised the system. We could show that the system is well suited for measurements of changes in hydrogen isotope ratios in ambient VOC due to chemical and physical processes in the atmosphere. First measurements of VOC in ambient air yielded promising results. Based on the hitherto experience we plan to improve the preconcentration system to further reduce water and carbon dioxide from the air samples, and test new adsorbents to improve the preconcentration and increase the spectrum of measurable compounds. In parallel, missing kinetic isotope effects will be measured as well as isotope ratios in VOC at the emission sources. These investigations will be followed by a longer-term measurement to investigate diurnal and seasonal variations. Additionally, new tools to interpret and apply the data will be developed. The proposed method is a sensitive tool to identify the origin of VOC, to study their atmospheric processing, to differentiate between impacts of mixing and chemical processes on their distribution as well as the residence times of the compounds. To our knowledge no measurements of stable hydrogen isotope ratios in atmospheric VOC are reported in the literature up to now. The new type of measurements will add another important piece of information to better understand chemical and physical processes in the atmosphere.