We present 14 CO 2 observations and related greenhouse gas measurements at a background site in Ireland (Mace Head, MHD) and a tall tower site in the east of the UK (Tacolneston, TAC) that is more strongly influenced by fossil fuel sources. These observations have been used to calculate the contribution of fossil fuel sources to the atmospheric CO 2 mole fractions; this can be done, as emissions from fossil fuels do not contain 14 CO 2 and cause a depletion in the observed 14 CO 2 value. The observations are compared to simulated values. Two corrections need to be applied to radiocarbon-derived fossil fuel CO 2 (ffCO 2 ): one for pure 14 CO 2 emissions from nuclear industry sites and one for a disequilibrium in the isotopic signature of older biospheric emissions (heterotrophic respiration) and CO 2 in the atmosphere. Measurements at both sites were found to only be marginally affected by 14 CO 2 emissions from nuclear sites. Over the study period of 2014-2015, the biospheric correction and the correction for nuclear 14 CO 2 emissions were similar at 0.34 and 0.25 ppm ffCO 2 equivalent, respectively. The observed ffCO 2 at the TAC tall tower site was not significantly different from simulated values based on the EDGAR 2010 bottom-up inventory. We explored the use of high-frequency CO observations as a tracer of ffCO 2 by deriving a constant ratio of CO enhancements to ffCO 2 ratio for the mix of UK fossil fuel sources. This ratio was found to be 5.7 ppb ppm −1 , close to the value predicted using inventories and the atmospheric model of 5.

We present 14 CO2 observations and related greenhouse gas measurements at a background site in Ireland and a tall-tower site in the east of the UK that is more strongly influenced by fossil fuel sources. These data have been used to calculate the contribution of fossil fuel sources to atmospheric CO2 mole fractions from the UK and Ireland. Corrections were calculated and applied for 14 CO2 emissions from the nuclear industry and other sources such as biospheric emissions that are in 15 disequilibrium with the atmosphere. Measurements at both sites were found to only be marginally affected by 14 CO2 emissions from nuclear sites. Over the study period of 2014 -2015, the biospheric correction and the correction for nuclear 14 CO2 emissions were similar, at 0.4 and 0.3 ppm fossil-fuel CO2 (ffCO2)-equivalent, respectively. The observed ffCO2 at the site was not significantly different from simulated values based on the EDGAR 2010 bottom-up inventory. We explored the use of high-frequency CO observations as a tracer of ffCO2 by deriving a constant COenhanced/ffCO2 ratio for the mix of UK fossil 20 fuel sources. This ratio was found to be 5.7 ppb ppm -1 , close to the value predicted using inventories and the atmospheric model of 5.1 ppb ppm -1 . The site in the east of the UK was strategically chosen to be some distance from pollution sources so as to allow for the observation of well-integrated air masses. However this, and the large measurement uncertainty in 14 CO2, lead to a large overall uncertainty in the ffCO2, being around 1.8 ppm compared to typical enhancements of 2 ppm.

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In this paper, we present the first data from an alternative extraction method for atmospheric 14CO2 analysis, based on the direct trapping of whole air samples onto a molecular sieve zeolite (13X) trap, incorporated into a commercially available automated graphitization system. Results are presented for both inter-laboratory comparison samples and an in-house reference standard. The in-house reference was used to calculate the standard deviation of measurements (2.0‰). This newly developed method will facilitate faster sample processing and therefore lower cost per analysis, critical for scaling up such studies.

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