Mass-independent isotopic compositions in oxygen containing molecules as a tool to investigate present and past changes in the Earth's oxidation capacity

The oxidation capacity of the atmosphere is of primary interest to the atmospheric community because it determines the lifetime of many trace species in the atmosphere that have implications in climate change and air quality. The chemical cycle of oxidants in the atmosphere is complex, and their short lifetimes make for large spatial and temporal heterogeneities. It is not clear how anthropogenic emissions are affecting this important parameter. In order to distinguish the anthropogenic impact, it is necessary to understand natural oxidant cycles. This has been a major obstacle because, with the exception of H₂O₂, these oxidants are not directly preserved in geological archives.; Measurement of the degree of the mass-independent fractionation (MIF) in the oxygen isotopes of atmospheric species provides a means to track photochemical processes in the atmosphere, and obtain an indirect picture of atmospheric oxidant concentrations. The oxygen isotope record of sulfate preserved in ice cores provides a record of the variation of sulfur oxidation mechanisms over various timescales. The present work focuses on the analysis of sulfate preserved in ice core samples covering the last full climate cycle (Vostok and Dome C, Antarctica) in addition to the investigation of the pre and post Industrial Revolution (Site A, Greenland). These studies contribute to the understanding of the role of sulfate aerosols in climate and elucidate anthropogenic effects on the atmospheric sulfur cycle and oxidation capacity of the Earth's atmosphere.; The major oxidant in the stratosphere is O(1D) derived from the photolysis of ozone at wavelengths less than 319 nm. The mass-independent composition of O₃ is transferred to CO₂ via isotopic exchange with O(1D). Isotopic measurements of stratospheric CO₂ thus provide an indirect method of tracing O(1D) number densities throughout the stratosphere. The isotopic anomaly in CO ₂ will increase with both increases in O(1D) number densities and with increased residence time in the stratosphere. Simultaneous measurements of CO₂ isotopes and the time dependent tracer SF₆ are presented here. Such measurements can be used to provide time-integrated number densities of O(1D) in the stratosphere, and can provide information on variations in the oxidation capacity with altitude.