Monitoring and quantifying CO2 emissions of isolated power plants from space
Abstract. Abstract: Top-down CO2 emission estimates based on satellite observations are potentially of great importance for independently verifying the accuracy of reported emissions and emission inventories. Difficulties in verifying these satellite-derived emissions arise from the fact that emission inventories often provide annual mean emissions while estimates from satellites are available only for a limited number of overpasses. Previous studies have derived CO2 emissions for power plants from OCO-2 and OCO-3 observations of their exhaust plumes, but the accuracy and the factors affecting these emissions are uncertain. We have selected only isolated power plants for this study, to avoid complications link to multiple sources in close proximity. We first compare the Gaussian plume model and cross-sectional flux methods for estimating CO2 emission of power plants. Then we examined the sensitivity of the emission estimates to possible choices for the wind field. For verification we have used power plant emissions that are reported on an hourly basis by the Environmental Protection Agency (EPA) in the United States. By using the OCO-2 and OCO-3 observations over the past four years we identified emission signals of isolated power plants and arrived at a total of 50 collocated cases involving 22 power plants. We correct for the time difference between the moment of the emission and the satellite observation. We found the wind field halfway the height of planetary boundary layer (PBL) yielded the best results. We found that the instantaneous satellite estimated emissions of these 50 cases and reported emissions display a weak correlation (R2=0.12). The correlation improves with averaging over multiple observations of the 22 power plants (R2=0.40). The method was subsequently applied to 106 power plants cases worldwide yielded a total emission of 1522 ± 501 Mt CO2/year, estimated to be about 17 % of the power sector emissions of our selected countries. The improved correlation highlights the potential for future planned satellite missions with a greatly improved coverage to monitor a significant fraction of global power plant emissions.
Xiaojuan Lin et al.
Xiaojuan Lin et al.
Xiaojuan Lin et al.
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Lin et al. “Monitoring and quantifying CO2 emissions of isolated power plants from space” builds off previous work on quantifying power plant emissions using OCO-2 and OCO-3 observations together with models. It is good to see this effort toward development of a more systematic and automated method that leverages what has been demonstrated by others in past case studies. Furthermore, the comparison between the Gaussian plume method (GPM) and Integrated Mass Enhancement (IME) method is a useful investigation that highlights the importance of the satellite coverage and resolution and the different nature of CO2 and CH4 plumes since the conclusion differs from that based on high spatial resolution CH4 observations in the literature. Overall, this is a useful study that helps to bring the field a step closer to the implementation of an operational system for CO2 anthropogenic emission monitoring as planned for CO2M. Following some minor revisions related to the specific points below, I would recommend its publication.
Line 43-44: These are not really the primary references regarding the difficulty to achieve accurate and detailed consumption data
Line 63: Reuter et al. (2019) derived emission estimates for power plants, urban areas and wild fires
Line 66: Nassar et al. (2022) https://www.frontiersin.org/articles/10.3389/frsen.2022.1028240/full is a key OCO-3 example worth mentioning
Line 71: Schwandner et al. 2017 is not the best choice of reference. Although the paper mentions power plants, it really focuses on XCO2 enhancements in an urban area (later understood to be topography related biases), while the only emission estimate is of volcanic emissions from one cloudy overpass
Line 74: “manually-selected” is perhaps a better descriptor than “hand-picked” (slang)
Line 79: Intermittency of U.S. sources has previously been studied by Hill and Nassar (2019) https://doi.org/10.3390/rs11131608 and Velazco et al. (2011) www.atmos-meas-tech.net/4/2809/2011/, so these two past studies should be cited.
Line 97: “≤ 1.29 x 2.25 km2” (It is worth noting that this is the maximum footprint size, since it is usually smaller due to solar angle and viewing geometry)
Line 97: “~52” degrees is recommended since the value can be exceeded by a few tenths of a degree in some cases
Line 111: daily global coverage before loss of data due to clouds
Line 119: This EPA link has annual power plant emission data, but is it the correct link for the hourly data too?
Line 257: Nassar et al. 2021 used the assumed height of the chimney plus an assumed 250 m for typical plume rise above the stack height
Line 295: For clarify, it would be helpful to specify that the x-axis is labelled with YYMMDD.
Line 374: Should revise language about GeoCarb as it has recently been cancelled by NASA.
Line 375: CO2M is a Copernicus mission with ESA and EUMETSAT involvement