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.
Methane emissions from livestock and agricultural wastes contribute globally more than 30% to the anthropogenic atmospheric methane source. Estimates of this number have been derived from respiration chamber experiments. We determined methane emission rates from a tracer experiment in a modern cow shed hosting 43 dairy cows in their accustomed environment. During a 24-hour period the concentrations of CH4, CO2, and SF6, a trace gas which has been released at a constant rate into the stable air, have been measured. The ratio between SF6 release rate and measured SF6 concentrations was then used to estimate the ventilation rate of the stable air during the course of the experiment. The respective tatio between CH4 or CO2 and SF6 concentration together with the known SF6 release rate allows us to calculate the CH4 (and CO2) emissions in the stable. From our experiment we derive a total daily mean CH4 emission of 441 L(STP) per cow (9 cows nonlactating), which is about 15% higher than previous estimates for German cows with comparable milk production obtained during respiration chamber experiments. The higher emission in our stable experiment is attributed to the contribution of CH4 release from about 50 m3 of liquid manure present in the cow shed in underground channels. Also, considering measurements we made directly on a liquid manure tank, we obtained an estimate of the total CH4 production from manure: The normalized contribution of methane from manure amounts to 12-30% of the direct methane release of a dairy cow during rumination. The total CH4 release per dairy cow, inncluding manure, is 521-530 L(STP) CH4 per day.
Long-term observations of the atmospheric trace gas sulfur hexafluoride (SF6) at four background monitoring stations, Neumayer, Antarctica (1986-1994), Cape Grim, Tasmania (1978-1994), Izana, Canary Islands (1991-1994) and Alert, Canada (1993-1994) are presented. These data sets are supplemented by two meridional profiles collected over the Atlantic Ocean (1990 and 1993) and occasional observations at the regional site Fraserdale, Canada (1994). The analytical system and the method of SF6 calibration are described. Compared with data from Neumayer and Izana reported earlier, measurements are updated for all sites until the end of 1994 and the precision has improved by more than a factor of 2. With the Cape Grim archived air samples, the atmospheric SF6 chronology is extended by 8 more years back to 1978. For the period from January 1978 to December 1994 the data confirm a stable and unbroken quadratic rise in tropospheric SF6 from 0.50 to 3.11 ppt in the southern hemisphere and for July 1991 to December 1994 from 2.69 to 3.44 ppt in the northern hemisphere. The global mean tropospheric increase rate in late 1994 was 0.225 ppt/yr (6.9%/yr). The long term trend and interhemispheric gradients are due to industrial production and emission, rising approximately linearly with time and located predominantly (94%) in the northern hemisphere. The interhemispheric exchange time (1.7+/-0.2 yr) derived from SF6 ground level observations when using a two-box model of the atmosphere is considerably larger if compared to the exchange time derived from two- and three-dimensional models (1.1 yr). The chemical and biological inertness of SF6 up to stratospheric conditions results in an atmospheric lifetime of more than 800 years and makes SF6 a powerful tool for modelling transport processes in the atmosphere. Moreover, the tropospheric SF6 chronology is a very valuable input function for mixing studies in linked compartments like the stratosphere, the hydrosphere and the cryosphere.
Our high precision data base of the global distribution of SF6 in the troposphere [Maiss et al., 1996] is used in a two-dimensional atmospheric transport model (2D-HD model) to study the behaviour of this new tracer in comparison to the classical global atmospheric transport tracer 85Krypton. The 2D-HD model grid has been deduced from the 3D Hamburg TM2 model with the same resolution in the vertical and meridional direction, and was designed to run on any standard personal computer. The same vertical convection scheme and wind field as in the TM2 model, reduced to two dimensions, were used in the calculations. In addition, the horizontal diffusion parameter of the model was fine-tuned by matching the model estimated mean meridional 85Krypton distribution with observations over the Atlantic ocean. For simulating global tropospheric SF6 concentrations, an almost linearly increasing SF6 source strength was applied since 1970. The latitudinal distribution of the SF6 source was assumed to be similar to the global electrical power production. Excellent agreement between SF6 model results and observations is achieved with the 85Krypton-tuned 2D-HD transport model with respect to the global meridional concentration distribution and particularly in mid to high northern latitudes. In the southern hemisphere, at the German Antarctic Neumayer station, a significant seasonal cycle of SF6 has been observed which is reproduced by the model, however with a smaller ampitude. This finding may point to possible shortcomings of the model's transport scheme when simulating the seasonality of stratosphere-troposphere exchange in high southern latitudes.