The first weekly 14CO2 flask has been filled at Mace Head, Ireland. Isotope sampling over the next 24 months will help to separate anthropogenic from biospheric contributions to the atmospheric carbon dioxide variations.

First weekly 14CO2 flask at Mace HeadThe first weekly 14CO2 flask (black flask) filled at Mace Head on 21st Jan 2014.

It is extremely difficult to separate observed atmospheric variations of CO2 mole fraction into its contributions from biospheric CO2 (e.g., plants and animals) and fossil fuel combustion, due to the natural variability of the CO2 signature. However, measurements of the ratio of two isotopes of carbon in CO2 may provide a solution. Isotopes are atoms of the same compound that have different masses (due to different numbers of neutrons in the nucleus). There are three major isotopes of carbon found in atmospheric CO2, the most common of which has a mass of 12 g/mol, and the less abundant of which have masses of 13 and 14 g/mol respectively. The heaviest of these isotopes, 14C has a relatively short lifetime (5000 years). Therefore, carbon that has been stored under the ground and converted over millions of years to fossil fuels (oil, gas, coal) has almost no 14C in it so that the CO2 released during fossil fuel combustion is free of the heavier isotope. This 14C-free fossil carbon effectively dilutes the atmospheric 14C/C ratio (Δ14C). Ultra-precise isotope 14CO2 analysis potentially provides a means to verify fossil CO2 emissions (CO2ff) calculated using economic inventories. GAUGE project scientists will take weekly flask samples at Mace Head, Ireland, to assess the background level of 14CO2 before it is influenced by mainland UK and weekly samples at a more polluted site in the eastern UK (Tacolneston, Norwich); together these measurements provide a longitudinal gradient over the UK, which GAUGE will use to assess the fossil fuel CO2 added to the atmosphere as it passes over the UK.

In collaboration with GAUGE, the isotope samples will be analysed by the University of Colorado INSTAAR laboratory for AMS Radiocarbon Preparation and Research. INSTARR began collaboration with the NOAA Earth System Research Laboratory (Boulder, Colorado) in 2003 with the aim of developing an ultra-precise Δ14CCO2 measurement capability in small (~2 L) samples of air, for implementation within the NOAA Cooperative Air Sampling Network. INSTAAR have maintained a long-term measurement repeatability of better than 1.8 ‰ (1-sigma) since 2004, as determined by repeat extraction and measurement of aliquots obtained from high-pressure surveillance cylinders [Turnbull et al., 2007; Lehman et al., 2012]. This equates to a detection capability for recently added fossil fuel derived in the atmosphere of less than 1 ppm, which is highly significant with respect to typical pollution signals [Miller et al., 2012]. They also maintain both manual [Turnbull et al., 2007] and automated [Turnbull et al., 2010] CO2 extraction lines, with an extraction capability of about 2000 samples/year. Currently, in collaboration with their AMS measurement partners at UC-Irvine, they perform about 1000 ultra-high precision 14CO2 measurements per year in connection with various atmospheric trace gas measurement programs around the world. Quantification of fossil fuel CO2 from observations requires paired measurements of both CO2 and 14CO2. CO2 measurements in the flasks will be obtained separately, leaving at least 2 L air (at standard temperature pressure) remaining for our analysis. INSTAAR also coordinate the International Atmospheric 14CO2 Intercomparison Program for the WMO.

The image shows the first weekly 14CO2 flask filled at Mace Head on 21st Jan 2014. Sampling will continue for the next 24 months.

Acronyms

References

Lehman, S.J., Miller, J.B. , Tans, P.P, Monzka, S.A., Sweeney, C., Andrews, A., Turnbull, J.C., and J. Southon (2012). 14CO2 Processing and Measurement Activities at CU-INSTAAR and NOAA/ESRL 16th WMO/IAEA Meeting on Carbon Dioxide, Other Greenhouse Gases, and Related Measurement Techniques (GGMT-2011), (Wellington, NZ, 25-28 Oct. 2011), World Meteorological Organization Global Atmosphere Watch Report No. 206, Geneva CH., p. 139-144.

Miller, J.B., Lehman,S.J., Montzka, S.A., Sweeney,C., Miller, B.R., Karion, A., Wolak, C., Miller, L., Dlugokencky, E.J., Southon, J., Turnbull, J.C. and P. P. Tans (2012). Linking emissions of fossil fuel CO2 and other anthropogenic trace gases using atmospheric 14CO2. Journal of Geophysical Research 117,D08302, 23 pp., doi:10.1029/2011JD017048.

Turnbull, J.C., Lehman, S.J., Miller, J.B., Tans, P., Sparks, R.J., and J. Southon (2007). A new high-precision 14CO2 time series for North American continental air. Journal of Geophysical Research doi:10.1029/2006JD008184, 10 pp.

Turnbull, J.C., Lehman, S.J., Morgan, S. and C. Wolak (2010). A new automated extraction system of 14C measurement in atmospheric CO2. Radiocarbon 52, 1261-9.