A New Analytical-Theoretical Method to Assess Past Changes in the Oxidising Capacity of Atmospheres

陆生植物是大气中挥发性有机化合物的最大排放者。这些化合物在运往极地的过程中发生化学转变。确定冰芯中的转化产物可以提供有关过去大气如何对类似于当前变化的气候突变作出反应的信息，从而有助于了解全球的不确定性。分析冰芯中的有机化合物是一项分析挑战，因为它们的浓度低，样品可用性有限。在这个项目中，我们的目标是将质谱分析能力推向极限，首次允许对冰芯进行连续流动分析，逐渐融化，以高时间分辨率测定档案中的有机化合物。这种新方法一旦投入使用，就可以应用于一系列冰芯，但对于较老的冰芯尤其有用，因为较深的冰芯分层紧密，可以检索使用传统方法可能丢失的古气候信息。考虑到目标分析物在其向极地地区的运输过程中在大气中发生转变，将建立一个结合反应性和全球运输的理论模型，以推断目标分析物在其大气寿命期间与之发生反应的大气氧化剂的平均浓度。理论框架的验证将通过比较氧化剂浓度的模型结果与近年来可用的直接测量结果来完成。

Terrestrial plants are the largest emitter of volatile organic compounds in the atmosphere. These compounds undergo chemical transformations during their transport to polar regions. Determining the transformation products in ice cores could provide information on how the past atmosphere reacted to abrupt climate changes, analogous to the present changes, thus contributing to knowledge around global uncertainties. Analysing organic compounds in ice cores represents an analytical challenge due to their low concentrations and limited sample availability. In this project, we aim at pushing mass spectrometry capability to its limits to allow, for the first time, for a continuous flow analysis of ice cores, gradually melted in continuous, for the determination of organic compounds with high time resolution in the archive. This novel method, once operational, can be applied to a range of ice cores but is especially useful for older ice cores, given the compact stratification of deeper segments, to retrieve paleoclimatic information that would otherwise be lost using traditional methods. Given that the target analytes are being transformed in the atmosphere during their transport to polar regions, a theoretical model, combining reactivity and global transport, will be developed to infer average concentrations of the atmospheric oxidants with which the target analytes have reacted during their atmospheric lifetime. Validation of the theoretical framework will be done by comparing model results of oxidant concentrations with direct measurements available for recent years.