Flux estimates of CO2, CH4, N2O, and CFCs over western Europe have been inferred from continuous atmospheric records of these species at the atmospheric research station of Mace Head, Ireland. We use radon (222Rn) which has a fairly uniform source over continents as a reference compound to estimate unknown sources of other species. The correlation between each species and 222Rn is calculated for a suite of synoptic events that have been selected in the Mace Head record over the period 1996/97. In the following, we describe the method and its uncertainties, and we establish data selection criteria that minimize the influence of local sources over Ireland, in the vicinity of the station, in order to select synoptic events originating from western Europe. We estimate western European flux densities of 45-30 103 kg C km-2 month-1 during wintertime for CO2, of 4.8-3.5 103 kg CH4 km-2 yr-1, 475-330 kg N2O km-2 yr-1, 2.5-1.8 kg CFC-11 km-2 yr-1 for CFC-11, and 4.2-2.9 kg CFC-12 km-2 yr-1 for CFC-12. Our estimates are independent, although in good agreement with those produced by inventories, except for CFC-11 where our estimate is much lower than the inventory.