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 (FRn) is a key parameter for estimating the source strength of any gas of interest (Fx), based on concentration differences observed over time in both, gas X (Dx) and 222Rn (DRn):
Fx = FRn Dx DRn-1
There are two approaches to obtain values for Dx and DRn . 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 FRn and DRn. The other approach to obtain values for Dx and DRn 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.