The Centre for Isotope Research (CIO) at the University of Groningen has operated a radiocarbon (14C) dating laboratory for almost 70 years. In 2017, the CIO received a major upgrade, which involved the relocation of the laboratory to new purpose-built premises, and the installation of a MICADAS accelerator mass spectrometer. This period of transition provides an opportunity to update the laboratory’s routine procedures. This article addresses all of the processes and quality checks the CIO has in place for registering, tracking and pretreating samples for radiocarbon dating. Complementary updates relating to radioisotope measurement and uncertainty propagation will be provided in other forthcoming publications. Here, the intention is to relay all the practical information regarding the chemical preparation of samples, and to provide a concise explanation as to why each step is deemed necessary.

[1] 14 C (radiocarbon) in atmospheric CO 2 is the most direct tracer for the presence of fossil-fuel-derived CO 2 (CO 2 -ff). We demonstrate the 14 C measurement of wine ethanol as a way to determine the relative regional atmospheric CO 2 -ff concentration compared to a background site (''regional CO 2 -ff excess'') for specific harvest years. The carbon in wine ethanol is directly back traceable to the atmospheric CO 2 that the plants assimilate. An important advantage of using wine is that the atmosphere can be monitored annually back in time. We have analyzed a total of 165 wines, mainly from harvest years 1990-1993 and 2003-2004, among , however, which can be used as a measure for the variability in atmospheric mixing and transport processes, show good agreement with those of the observations all over Europe. Correcting for interannual variations using modeled data produces a regional CO 2 -ff excess signal that is potentially useful for the verification of trends in regional fossil fuel consumption. In this fashion, analyzing 14 C from wine ethanol offers the possibility to observe fossil fuel emissions back in time on many places in Europe and elsewhere.

This study investigates the accuracy of the radiocarbon-based calculation of the biogenic carbon fraction for different biogas and biofossil gas mixtures. The focus is on the uncertainty in the 14 C reference values for 100% biogenic carbon and on the 13 C-based isotope fractionation correction of the measured 14 C values. The separately (AMS) measured CO 2 and CH 4 fractions of 8 different biogas samples showed 14 C values between 102‰ and 116% (pMC). The δ 13 C values of these samples varied between -6‰ and +31‰ for the CO 2 fraction and between -28‰ and -62‰ for the CH 4 fraction. The uncertainty in calculated biogenic carbon fractions due to uncertainty in the 14 C reference values depends on the available information about the origin of the used biogenic materials. It varies between ±0.5% and ±3.5% (absolute) depending on the type of biogas. A method is proposed to minimize this uncertainty for different groups of biogases. The calculated biogenic carbon fraction deviates up to ±2.5% for biofossil gas mixtures, if the applied isotope fractionation correction is based on the δ 13 C value of the mixed biofossil sample instead of the biogenic δ 13 C value. Combination of both error sources shows that the uncertainty in the calculated biogenic carbon fraction varies between ±0.7% and ±4.5%, depending on the type of biogas in the sample.

No abstract

This article presents results from the first 3 rounds of an international intercomparison of measurements of  14 CO 2 in liter-scale samples of whole air by groups using accelerator mass spectrometry (AMS). The ultimate goal of the intercomparison is to allow the merging of  14 CO 2 data from different groups, with the confidence that differences in the data are geophysical gradients and not artifacts of calibration. Eight groups have participated in at least 1 round of the intercomparison, which has so far included 3 rounds of air distribution between 2007 and 2010. The comparison is intended to be ongoing, so that: a) the community obtains a regular assessment of differences between laboratories; and b) individual laboratories can begin to assess the long-term repeatability of their measurements of the same source air. Air used in the intercomparison was compressed into 2 high-pressure cylinders in 2005 and 2006 at Niwot Ridge, Colorado (USA), with one of the tanks "spiked" with fossil CO 2 , so that the 2 tanks span the range of  14 CO 2 typically encountered when measuring air from both remote background locations and polluted urban ones. Three groups show interlaboratory comparability within 1‰ for ambient level  14 CO 2. For high CO 2 /low  14 CO 2 air, 4 laboratories showed comparability within 2‰. This approaches the goals set out by the World Meteorological Organization (WMO) CO 2 Measurements Experts Group in 2005. One important observation is that single-sample precisions typically reported by the AMS community cannot always explain the observed differences within and between laboratories. This emphasizes the need to use long-term repeatability as a metric for measurement precision, especially in the context of long-term atmospheric monitoring.