Atmospheric radiocarbon measurements to quantify CO 2 emissions in the UK from 2014 to 2015

Abstract. We present 14 CO 2 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 CO 2 mole fractions from the UK and Ireland. Corrections were calculated and applied for 14 CO 2 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 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 0.4 and 0.3 ppm fossil-fuel CO 2 (ffCO 2 )-equivalent, respectively. The observed ffCO 2 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 ffCO 2 by deriving a constant CO enhanced / 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 5.1 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 CO 2 , lead to a large overall uncertainty in the ffCO 2 , being around 1.8 ppm compared to typical enhancements of 2 ppm.