Long-term atmospheric 14CO2 observations are used to quantify fossil fuel-derived CO2 concentrations at a regional polluted site, and at a continental mountain station in southwest Germany. Fossil fuel CO2 emission rates for the relevant catchment areas are obtained by applying the Radon-Tracer-Method. They compare well with statistical emissions inventories but reveal a larger seasonality than earlier assumed, thus contributing significantly to the observed CO2 seasonal cycle over Europe. Based on the present approach, emissions reductions on the order of 5--10% are detectable for catchment areas of several hundred kilometres radius, as anticipated within a five-years commitment period of the Kyoto Protocol. Still, no significant change of fossil fuel CO2 emissions is observed at the two sites over the last 16 years.