Atmospheric radiocarbon measurements to quantify CO<sub>2</sub> emissions in the UK from 2014 to 2015
Abstract. We present 14CO2 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 14CO2 emissions from the nuclear industry and other sources such as biospheric emissions that are in disequilibrium with the atmosphere. Measurements at both sites were found to only be marginally affected by 14CO2 emissions from nuclear sites. Over the study period of 2014–2015, the biospheric correction and the correction for nuclear 14CO2 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 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 14CO2, lead to a large overall uncertainty in the ffCO2, being around 1.8 ppm compared to typical enhancements of 2 ppm.