Non-CO₂ greenhouse gases (CH₄, N₂O, SF₆, halocarbons) are responsible for 37 % of the anthropogenic contribution to global warming. Some of these gases (N₂O, SF₆, chlorinated and brominated halocarbons) are in addition destructive to the stratospheric ozone layer. Regional emission estimates of non-CO₂ greenhouse gases are currently much more uncertain than for CO₂. Mostly, they are based on ‘bottom-up’ approaches relying on inventories of known sources and expected emission functions. The ²²²Rn flux map of Europe produced in the preceding project permits today a more reliable real-world assessment by the ²²²Rn tracer method, a so-called ‘top-down’ approach. In previous studies, source strength of ²²²Rn has been a major uncertainty. Substantial reduction of uncertainty has been achieved so far and further improvements are aimed for in the present project. Future improvements include in particular a better temporal resolution of the ²²²Rn flux map. Current developments within the EU-driven European Radiological Data Exchange Platform (EURDEP) open the possibility for quasi real-time updates of the European ²²²Rn source term. The source strength of ²²²Rn (F_Rn) is a key parameter for estimating the source strength of any gas of interest (F_x), based on concentration differences observed over time in both, gas X (D_x) and ²²²Rn (D_Rn):

F_x = F_Rn D_x D_Rn^-1

There are two approaches to obtain values for D_x and D_Rn . One is during pollution events at otherwise remote ‘background’ stations. This approach is followed in an associated project at Jungfraujoch (main applicant: Stefan Reimann, EMPA), where we will contribute the parameters F_Rn and D_Rn. The other approach to obtain values for D_x and D_Rn relies on changes in mixing layer height as observed during nocturnal inversions and will be applied to the measurement of non-CO₂ greenhouse gases in the central part of Eastern Europe (Hungary). Emissions from this region just east of the Alpine Ridge are highly uncertain and can not be detected at Jungfraujoch using the first approach.