Atmospheric radiocarbon measurements to quantify CO<sub>2</sub> 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 (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.

Analysis of regional CO<sub>2</sub> contributions at the high Alpine observatory Jungfraujoch by means of atmospheric transport simulations and δ<sup>13</sup>C

“…The stable oxygen isotope ratio of CO2, δ 18 O-CO2, is, aside of the carbon cycle, subject to the global water cycle (e.g., Welp et al, 2011) due to the isotope exchange between water and CO2 and thus ambiguous as CO2 115 tracer. However, the radiocarbon signature may be used to quantify fossil fuel contributions to atmospheric CO2, as done by e.g., Levin et al (2003), Vogel et al (2010), Turnbull et al (2015), Berhanu et al (2017), or Wenger et al (2019). The  14 C allows primarily for discrimination of fossil versus ecosystem carbon.…”

“…Yet, to date, few studies have performed hourly-scale regional simulations of CO2 concentration and/or provide "model-based" atmospheric δ 13 C-CO2 or mixed isotope source signatures (δ 13 Cm) for a comparison with 130 observations. The available studies currently include two ground-based urban locations (Pugliese-Domenikos et al (2019) and Vardag et al (2016)), and one rural tall tower location (Wenger et al, 2019).…”

“…However, they were limited regarding either the length of the observation period (few months in Downsview), and/or the stringent data filtering (e.g., Vardag et al (2016) discarded 85 % of the data and 555 biased the urban data sets towards night-time observations, Pugliese-Domenikos et al, 2019 discarded 80% of the data for their isotopic mass balance approach). Contrary, the tall tower study in rural England was challenged by a low signal-to-background ratio (ΔCO2 reaching around 20 ppm), and isotope measurements were performed at low (weekly) time-resolution, although simulations are provided on hourly-scale (Wenger et al, 2019).…”

“…In comparison to the results from JFJ, Pugliese-Domenikos et al (2019) reported an r = 0.58 (r 2 = 0.3), a 560 root mean square error (RMSE) of 1.05 ‰ and a mean bias of 0.04 ‰ for a single month (January) for δ 13 C-CO2. Wenger et al (2019) do not provide any regression parameters for their model-observation comparisons; however, they observed large uncertainties in the δ 13 C-CO2 estimation using a Monte Carlo approach. They related a part of their uncertainty for the δ 13 C-CO2 estimates to the influence of ecosystem processes and the dominance of ecosystem fluxes on the regional CO2 observations and simulations at the rural tall tower site.…”

Ground-Based Atmospheric Measurements of CO:CO2 Ratios in Eastern Highland Rim Using a CO Tracer Technique

“…Despite the effectiveness and superior capability of the radioactive technique in unambiguously deciphering the contribution of fossil-fuel CO 2 signals in urban CO 2 emissions, the technique is expensive and laborous, hindering its frequent use by researchers. In many instances where the 14 C technique has been adapted, the CO tracer technique is employed as a complementary method to enhance spatial and temporal coverage. ,,,,,,,, …”