[1] Long-term atmospheric 14 CO 2 observations are used to quantify fossil fuel-derived CO 2 concentrations at a regional polluted site, and at a continental mountain station in southwest Germany. Fossil fuel CO 2 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 CO 2 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 fiveyears commitment period of the Kyoto Protocol. Still, no significant change of fossil fuel CO 2 emissions is observed at the two sites over the last 16 years.

Abstract. We present a 3 year record of continuous gas chromatographic nitrous oxide (N20) observations performed at the urban station Heidelberg (Germany) together with weekly flask data from a remote continental site, Schauinsland (Black Forest, Germany), and two-weekly integrated data from the maritime background station Izafia (Canary Islands). These data are supplemented by continuous atmospheric radon 222 observations. m -2 h -1. These local measurements of source strengths are able to resolve large temporal variations of emission strengths, often accompanied by high spatial variability. However, the inhomogeneity and large temporal variation of many often poorly understood local N20 emissions make an upscaling, and thus regional budgeting, very doubtful. Mean rates of increaseRegional studies that fill the gap between the global and local scales are therefore needed to improve our estimates of emission inventories on the national level. Recently, a few such investigations were undertaken to budget greenhouse gas emissions using atmospheric observations at continental sites, Radon 222 is a radioactive noble gas with a half-life T1/2 of 3.8 days, i.e., a lifetime of 5.5 days, that is produced at relatively constant rates in all soils and released to the atmosphere, where it is diluted by (atmospheric) transport and radioactive decay. The 222Rn flUX from ocean surfaces is negligible. The atmospheric 222Rn activity can thus be used to parameterize continental air mass residence times and also the dilution of ground level emissions in the atmospheric surface layer driven 5507

Since 1972, the German Environment Agency (UBA) has been measuring continuously CO2 concentration at Schauinsland station (southwest Germany, 1205 m asl). Because of its vicinity to biogenic and anthropogenic sources and sinks, the Schauinsland CO2 record shows considerable variability. In order to remove these disturbances and derive the large‐scale representative “background” CO2 level for the respective area (southwest Germany) we perform rigorous data selection based on wind speed and time of day. During the past 30 years, the selected CO2 mixing ratios increased by 1.47 ppm per year, following the mean trend in midlatitudes of the Northern Hemisphere. The average seasonal cycle (peak to peak) amplitude has decreased slightly from 13.8 ± 0.6 ppm in the first decade (1972–1981) to 12.8 ± 0.7 ppm in the last two decades (1982–2001). This is opposite to other northern latitude sites and is attributed to the decrease of fossil fuel CO2 emissions in the catchment area (southwest Germany and France) and its respective change in the seasonal variation. Except for May and June, monthly mean CO2 mixing ratios at Schauinsland are higher by up to 8 ppm if compared to marine boundary layer air, mainly as a consequence of fossil fuel CO2 emissions in Europe. The CO2 measurements when combined with continuous 222Rn observations at the same site allow an estimate of the net CO2 flux in the catchment area of Schauinsland: Mean seasonal fluxes compare very well with estimates from a process‐oriented biosphere model (SIB‐2) as well as from an inverse modeling approach [Peylin et al., 2000]. Annual CO2 fluxes vary by more than a factor of 2, although anthropogenic fossil fuel CO2 emissions show interannual variations of only about 10%. The major part of the variability must therefore be associated to interannual changes of biospheric uptake and release, which are on the order of the total fossil fuel emissions in the same area. This has to be taken into account when reliably quantifying and verifying the long‐term carbon balance and emission reduction targets in the European Union.

4-year records of gas chromatographic carbon dioxide and methane observations from the continental mountain station Schauinsland in the Black Forest (Germany) are presented. These data are supplemented by continuous atmospheric 222 Radon observations. The raw data of C02 concentration show a large seasonal cycle of about 16 ppm with monthly mean wintertime enhancements up to 10 ppm higher and summer minima up to 5 ppm lower than the maritime background level in this latitude. These offsets are caused by regional and continental scale CO2 sources and sinks. The mean CH4 concentration at Schauinsland is 31 ppb higher than over the Atlantic ocean, due to the European continent acting as a net source of atmospheric CH4 throughout the year. No significant seasonal cycle of methane has been observed. The long term C02 and CH4 increase rates at Schauinsland are found to be similar to background stations in the northern hemisphere, namely 1.5 ppm C02 yr" 1 and 8 ppb CH4 yr-1. On the time scale of hours and days, the wintertime concentrations of all three trace gases are highly correlated, the mean ratio of CH4/C02 is 7.8 +1.0 ppb/ppm. The wintertime monthly mean concentration offsets relative to the maritime background level show a CH4/C02 ratio of 6.5 + 1.1 ppb/ppm, thus, not significantly different from the short term ratio. Using the win tertime regressions of C02 and 222 Radon respectively CH4 and 222 Radon we estimate winter time C02 flux densities of 10.4 + 4.3 mmol C02 m-2 h-1 (from monthly mean offsets) and 6.4 + 2.5 mmol C02 m~2 h" 1 (from short term fluctuations) and winter time methane flux densities of 0.066 + 0.034mmol CH4 m~2 h" 1 (from monthly mean offsets) and 0.057 + 0.022 mmole CH4 m~2 h" 1 (from short term fluctuations). These flux estimates are in close agreement to C02 respectively CH4 emission inventories reported for Germany from statistical data.

The radioactive decay of radon and its progeny can lead to ionization of air molecules and consequently influence aerosol size distribution. In order to provide a global estimate of the radon-related ionization rate, we use the global atmospheric model ECHAM5 to simulate transport and decay processes of the radioactive tracers. A global radon emission map is put together using regional fluxes reported recently in the literature. Near-surface radon concentrations simulated with this new map compare well with measurements. <br><br> Radon-related ionization rate is calculated and compared to that caused by cosmic rays. The contribution of radon and its progeny clearly exceeds that of the cosmic rays in the mid- and low-latitude land areas in the surface layer. During cold seasons, at locations where high concentration of sulfuric acid gas and low temperature provide potentially favorable conditions for nucleation, the coexistence of high ionization rate may help enhance the particle formation processes. This suggests that it is probably worth investigating the impact of radon-induced ionization on aerosol-climate interaction in global models