Challenges faced when using radiocarbon measurements to estimate fossil fuel emissions in the UK.

Abstract:

Estimating the anthropogenic component of carbon dioxide emissions from direct atmospheric measurements is difficult, due to the large natural carbon dioxide fluxes. One way of determining the fossil fuel component of atmospheric carbon dioxide is the use of radiocarbon measurements. Whilst carbon reservoirs with a reasonably fast carbon exchange rate all have a similar radiocarbon content, fossil fuels are completely devoid of radiocarbon due to their age. Previous studies have ¹⁴CO₂ (UK) this approach is compromised by the high density of ¹⁴CO₂ emitting nuclear power plants. Of the 16 nuclear reactors in the UK, 14 are advanced gas cooled reactors, which have one of the highest ¹⁴CO₂ emission rates of all reactor types. These radiocarbon emissions not only lead to a serious underestimation of the recently added fossil fuel CO₂, by masking the depletion of ¹⁴C in CO₂, but can in fact overshadow the depletion by a factor of 2 or more. While a correction for this enhancement can be applied, the emissions from the nuclear power plants are highly variable, and an accurate correction is therefore not straightforward. We present the first attempt to quantify UK fossil fuel CO₂ emissions through the use of ¹⁴CO₂. We employ a sampling strategy that makes use of a Lagrangian particle dispersion model, in combination with nuclear industry emission estimates, to forecast “good” sampling times, in an attempt to minimize the correction due to emissions from the nuclear industry. As part of the Greenhouse gAs Uk and Global Emissions (GAUGE) project, ¹⁴CO₂measurements are performed at two measurement sites in the UK and Ireland, as well as during science flights around the UK. The measurement locations have been chosen with a focus on high emitting regions such as London and the Midlands.

We discuss the unique challenges that face the determination of fossil fuel emissions through radiocarbon measurements in the UK and our sampling strategy to deal with them. In addition we present the first results of our ground based measurements, and their implications for how radiocarbon measurements might be used, even in seemingly impractical locations.