Impact of atmospheric turbulence on the accuracy of point source emission estimates using satellite imagery

Abstract

Observation-based monitoring of the status of greenhouse gas emissions goals set at the 2015 Paris Climate Summit is critical to provide timely, accurate and precise information on the progress towards these goals. Observations also permit the identification of potential deviations from the adopted policies that could compromise the efforts to reduce the future impact of pollutants on the climate. Current remote sensing capabilities of atmospheric CO2 have demonstrated the ability to estimate emissions from the strongest sources of CO2 based on imagery of individual plumes in conjunction with wind speed estimates. However, a realistic evaluation of the accuracy of the obtained estimates is essential. Here, we examine how the stochastic nature of daytime atmospheric turbulence affects the estimation of CO2 emissions from a lignite coal power plant in Bełchatów, Poland. For this investigation, we use a high-resolution (400 m × 400 m × 85 levels) atmospheric model set up in a realistic configuration. We demonstrate that persistent structures in the downwind concentration fields of emitted plumes can cause significant uncertainties in the retrieved fluxes, on the order of 10 % of the total source strength, when the commonly used cross-sectional mass-flux (CSF) method is applied with short distances between individual estimates. These form a significant contribution to the overall uncertainty which remains unavoidable in the presence of atmospheric turbulence. Furthermore, we applied temporally tagged tracers for the decomposition of the plume variability into its constituent parts. These tracers helped us to explain why spatial scales of variability in plume intensity are far larger than the size of turbulent eddies - a finding that challenges previous assumptions.