Atmospheric Verification of Point Source Fossil Fuel CO2 Emissions

Abstract:

Large point sources (electricity generation and large-scale industry) make up roughly one third of all fossil fuel CO₂ (CO₂ff) emissions. Currently, these emissions are determined from self-reported inventory data, and sometimes from smokestack emissions monitoring, and the uncertainty in emissions from individual power plants is about 20%. We examine the utility of atmospheric ¹⁴C measurements combined with atmospheric transport modelling as a tool for independently quantifying point source CO₂ff emissions, to both improve the accuracy of the reported emissions and for verification as we move towards a regulatory environment.

We use the Kapuni Gas Treatment Facility as a test case. It is located in rural New Zealand with no other significant fossil fuel CO₂ sources nearby, and emits CO₂ff at ~0.1 Tg carbon per year. We use several different sampling methods to determine the ¹⁴C and hence the CO₂ff content downwind of the emission source: grab flask samples of whole air; absorption of CO₂ into sodium hydroxide integrated over many hours; and plant material which faithfully records the ¹⁴C content of assimilated CO₂. We use a plume dispersion model to compare the reported emissions with our observed CO₂ff mole fractions. We show that the short-term variability in plume dispersion makes it difficult to interpret the grab flask sample results, whereas the variability is averaged out in the integrated samples and we obtain excellent agreement between the reported and observed emissions, indicating that the ¹⁴C method can reliably be used to evaluated point source emissions.