Aircraft-based in situ measurements of CH4 and CO2 downstream of European and Asian urban centres at local to synoptic scales

In urban areas large amounts of carbon dioxide (CO2) and methane (CH4), the two most important anthropogenic greenhouse gases (GHG), are released. The contribution of individual sources and their spatial distribution are still unknown but need to be better understood in order to reliably predict future climate impacts. In this thesis high-accuracy airborne in situ measurements, using cavity ring-down spectroscopy, were carried out to analyse the impact of urban CO2 and CH4 emissions on the local to synoptic scale GHG distribution. The focus is on the German capital Berlin and on megacities in Europe and Asia. Based on the local case study, the GHG plume from Berlin was detected above the atmospheric background and the estimated top-down emission rates, using a mass balance method, were used to validate bottom-up emissions and to reveal missing sources in inventories. On the synoptic scale, European and Asian urban GHG signatures could be identified despite the larger sampling distance from the cities and thus the increased inmixing of background air. The origin of urban air masses was verified by numerical model simulations and simultaneous measurements of short-lived species