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 Schauinsland 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 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 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^-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/CO₂ is 7.8 ± 1.0 ppb/ ppm. The wintertime monthly mean concentration 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 m^-2 h^-1 (from monthly mean offsets) and 6.4 ± 2.5 mmol CO₂ m^-2 h^-1 (from short term fluctuations) and winter time methane flux densities of 0.066 ± 0.034 mmol 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 CO₂ respectively CH₄ emission inventories reported for Germany from statistical data.