Carbon dioxide and methane in continental Europe: a climatology, and 222Radon-based emission estimates

4-year records of gas chromatographic carbon dioxide and methane observations from the continental mountain station Schauninsland in the Black Forest (Germany) are presented. These data are supplemented by continuous atmospheric 222Radon observations. The raw data of CO2 concentration show a large seasonal cycle of about 16ppm with monthly mean wintertime enhancements up to 10ppm 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 31ppb 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 cylce of methane has been observed. The long term CO2 and CH4 increase rates at Schauinsland are found to be similar to background stations in the northern hemisphere, namely 1.5 ppm CO2/yr and 8 ppb CH4/yr. On the time scale of hours and days, the wintertime concentrations of all three trace gases are highly correlated, the mean ratio of CH4/CO2 is 7.8+/-1.0ppb/ppm. The wintertime monthly mean concentrations offsets relative to the maritime background level show a CH4/CO2 ratio of 6.5+/-1.1 ppb/ppm, thus, not significantly different from the short term ratio. Using the wintertime regressions of CO2 and 222Radon respectively CH4 and 222Radon we estimate winter time CO2 flux densities of 10.4+/-4.3 mmol CO2/m2/hr (from monthly mean offsets) and 6.5+/-2.5 mmol CO2 /m2/hr (from short term fluctuations) and winter time methane flux densities of 0.066+/-0.034 mmol CH4 /m2/hr (from monthly mean offsets) and 0.057 +/-0.022 mmole CH4/m2/hr (from short term fluctuations). These flux estimates are in close agreement to CO2 respectively CH4 emission inventories reported for Germany from statistical data