We present a three-year record of continuous gas chromatographic nitrous oxide (N2O) 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 Izaña (Canary Islands). These data are supplemented by continuous atmospheric radon-222 observations. Mean rates of increase of N2O of 0.70–0.78 ppb/yr were observed over the continent and in maritime background air (Izana). The well-mixed continental mixing ratio was found to be higher by only 1.1 ppb (Schauinsland) and 2.4 ppb (Heidelberg) than for maritime background air. Specially tailored data selection of the Heidelberg record allowed the changing influence of a regional N2O point source (adipic acid production, BASF AG) to be clearly identified. The radon (222Rn) tracer method was applied to nighttime N2O observations at Heidelberg to estimate mean regional emissions, which changed from (161±32) µg N2O-N/m2/h in 1996/1997 to (77±10) µg N2O-N /m2/h1 in 1998 as a consequence of 90% emission reduction from BASF. An estimate of the continental N2O flux from southwestern Europe based on further selected Heidelberg data (only well-mixed, late afternoon situations) and observations from the Schauinsland station yielded mean N2O fluxes of (43±5) µg N2O-N m–2h–1 and (42±4) µg N2O-N /m2/h1. These results compare well with statistical emissions inventories, when taking into account possible systematic errors of the radon tracer method of 30-35%.
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 considerably variability. In order to remove these disturbances and derive the large-scale representative "background" CO2 levels 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 rations 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 8ppm 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 modelling approach (Peylin et al, 2000). Annual CO2 fluxes vary by more than a factor of 2, although atnthropogenic 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 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.
Long-term atmospheric 14CO2 observations are deployed to quantify fossil fuel derived CO2 concentrations at a regional polluted site, and at a continental mountain station in south-west Germany. Fossil fuel CO2 emission rates for the relevant catchment areas are obtained by applying the Radon-Tracer-Method. They are shown to compare well with statistical emissions inventories but reveal a larger seasonality than assumed earlier, 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.