Quantifying CO2 emissions of power plants with the CO2M mission

Abstract

<p>In this study, we analyse the capability of the Copernicus CO<sub>2</sub> monitoring (CO2M) satellite mission to quantify the CO<sub>2</sub> emissions of individual power plants, which is one of the prime goals of the mission. The study relies on synthetic CO<sub>2</sub> and NO<sub>2</sub> satellite observations over parts of the Czech Republic, Germany and Poland and quantifies the CO<sub>2</sub> and NO<sub>x</sub> emissions of the 15 largest power plants in that region using a data-driven mass-balance approach.</p><p>The synthetic observations were generated for six CO2M satellites based on high-resolution simulations of the atmospheric transport model COSMO-GHG. To identify the emission plumes, we developed a plume detection algorithm that identifies the location, orientation and extent of multiple plumes from CO2M's NO<sub>2</sub> observations. Afterwards, a mass-balance approach was applied to individual plumes to estimate CO<sub>2</sub> and NO<sub>x</sub> emissions by fitting Gaussian curves to the across-plume signals. Annual emissions were obtained by interpolating the temporally sparse individual estimates applying a low-order spline fit.</p><p>Individual CO<sub>2</sub> emissions were estimated with an accuracy <65% for a source strength >10 Mt CO<sub>2</sub> yr<sup>-1</sup>, while NO<sub>x</sub> emissions >10 kt NO<sub>2</sub> yr<sup>-1 </sup>were estimated with <56% accuracy. NO<sub>2</sub> observations were essential for detecting the plume and constraining the shape of the Gaussian curve. With three CO2M satellites, annual CO<sub>2</sub> emissions were estimated with an uncertainty <30% for source strengths larger than 10 Mt yr<sup>-1</sup>, which includes an estimate of the uncertainty in the temporal variability of emissions. Annual NO<sub>x</sub> emissions were estimated with an uncertainty <21%. Since NO<sub>x</sub> emissions can be determined with better accuracy, estimating CO<sub>2</sub> emissions directly from the NO<sub>x</sub> emissions by applying a representative CO<sub>2</sub>:NO<sub>x</sub> emission ratio  seems appealing but this approach was found to suffer significantly from the high uncertainty in the  CO<sub>2</sub>:NO<sub>x</sub> emission ratios determined from the same CO2M observations.</p><p>Our study shows that CO2M should be able to quantify the emissions of the 400 largest point sources globally with emissions larger than 10 Mt yr<sup>-1</sup> that account for about 20 % of global anthropogenic CO<sub>2</sub> emissions. However, the mass-balance approach used here has relatively high uncertainties that are dominated by the uncertainties in the estimated CO<sub>2</sub> background and the wind speed in the plume, and uncertainties associated with the sparse temporal sampling of the varying emissions. Estimates could be significantly improved if these parameters can be better constrained, e.g., with atmospheric transport simulations and independent observations.</p>