High-precision measurements of atmospheric oxygen play an increasingly important role in our understanding of the global carbon cycle and its feedbacks on the Earth’s climate. In combination with CO2 measurements, they allow partitioning of global oceanic and terrestrial sinks of anthropogenic CO2. In addition, influences from biospheric processes and anthropogenic emissions on observed CO2 variations can be distinguished using simultaneously measured O2 mixing ratios, since these processes have different O2:CO2 ratios. Over the past decade, the global network of stations monitoring atmospheric O2 in addition to CO2 has been growing continuously and also become more representative due to the addition of continental stations. Data from these stations allow better constraining of fluxes from regional to continental scales, but due to the proximity of highly variable local (e.g. anthropogenic) sources and sinks additional effort is needed to interpret the measurements. This thesis deals with two aspects that are important for improving the ability to utilize those data: First, the characterization of anthropogenic sources, their spatial and temporal variability and their influence on the atmospheric composition, and second, the use of airborne measurements to characterize the spatial variability of fluxes in between the ground-based monitoring stations. In the first part of this thesis, the possibility to use simultaneous atmospheric O2 and CO2 measurements for identifying different types of emission sources is investigated. The second part deals with the use and improvement of airborne measurements of atmospheric oxygen, by presenting results from an aircraft campaign in the Amazon forest and the development of a new instrument for in-situ O2 measurements onboard research aircraft.