Delta 14 CO2 records from two sites in Central Europe

All air samples at Schauinsland have been collected from a ventilated intake stack approximately 7m above the ground. Bi-weekly integrated CO2 samples from about 15-20 m^3 of air have been continuously collected by dynamic quantitative absorption in carbonate-free sodium hydroxide (NaOH) solution. Air has been pumped through a rotating glass tube filled with a packed bed of Raschig rings (hard glass) to enlarge the surface of the absorbing NaOH solution (200 ml of 4 normal NaOH). The CO2 absorption is quantitative and samples represent mean values of 10 days to 2 weeks. In the laboratory, the samples are extracted from the NaOH solution in a vacuum system by adding hydrochloric or sulfuric acid. 13C analyses of the CO2 are by mass spectrometry and 14C analyses are by high precision proportional counting, after purification of the CO2 sample over charcoal (Schoch et al. 1980, Kromer and Munnich 1992). Delta 13C values are given relative to the V-PDB standard (Hut 1987) with the overall precision of a single analysis reported to be +/- 0.15 per mil (Levin and Kromer 1997). Delta 14C data are given relative to the NIST oxalic acid activity corrected for decay (Stuiver and Polach 1977) with the precision of a single delta 14C measurement reported to be +/- 3-5 per mil (Levin and Kromer 1997). This time series from Schauinsland coupled with the record from Vermunt, offers 35 years of 14CO2 since the nuclear test ban treaty in 1962. Levin et al. (1985) consider this time series from Schauinsland to be representative of the higher altitude 14CO2 level over central Europe. On the basis of close agreement between the 14CO2 records from Schauinsland and Vermunt, Levin et al. (1985) suggest the two records are indicative of the 14CO2 level of tropospheric CO2 above Central Europe. The sampling at Vermunt was discontinued in 1983. During sampling from 1959 to 1983, the sampling methods were modified twice (Levin et al. 1985). From 1959 through November 1965, three dishes with 1.5 L of 0.5 normal sodium hydroxide (NaOH) carbonate-free solution were exposed to the atmosphere for ~3 days, and the atmospheric CO2 absorbed during that time was recovered by acid evolution. From November 1965 through May 1975, samples were collected by pumping fresh air continuously for 10 days through a box containing 1.5 L of a 0.5 normal NaOH solution. The method has been described by Munnich and Vogel (1959). From May 1975 to the time sampling stopped, a technique described by Levin et al. (1980) was used. Air was pumped through a rotating glass tube filled with a packed bed of Raschig rings (hard glass) to enlarge the surface of the absorbing NaOH solution (200 ml of 4 normal NaOH). The CO2 absorption was quantitative and samples represent mean values of 10 days to 2 weeks. In the laboratory, the samples were extracted from the NaOH solution in a vacuum system by adding hydrochloric or sulfuric acid. The CO2 gas samples were purified over charcoal and counted in a proportional counter (Schoch et al. 1980). Delta 14C values are given relative to the NIST oxalic acid activity corrected for decay (Stuiver and Polach 1970). The long-term delta 14CO2 record from Vermunt exhibits the same delta 14CO2 decline seen at other sampling locations around the world. According to Levin et al. (1985), the Vermunt record is representative of the higher altitude 14CO2 level over Central Europe. Levin et al. (1985) reported marked seasonal variations in the 14CO2 levels at Vermunt in the early 1960s, up to ca delta 14CO2 = 200 per mil, resulting mainly from springtime injections of bomb 14CO2 from the stratosphere. Levin et al. (1985) reported that the peak-to-peak variations in delta 14CO2 since 1976 at Vermunt were ~20 per mil, due partly to seasonal variations of the contribution of fossil fuel CO2.