A global map of emission clumps for future monitoring of fossil fuel CO₂ emissions from space

• Main Authors: Y. Wang, P. Ciais, G. Broquet, F.-M. Bréon, T. Oda, F. Lespinas, Y. Meijer, A. Loescher, G. Janssens-Maenhout, B. Zheng, H. Xu, S. Tao, K. R. Gurney, G. Roest, D. Santaren, Y. Su
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-05-01
• Series: Earth System Science Data
• Online Access: https://www.earth-syst-sci-data.net/11/687/2019/essd-11-687-2019.pdf
• ISSN: 1866-3508; 1866-3516

<p>A large fraction of fossil fuel <span class="inline-formula">CO₂</span> emissions emanate from “hotspots”, such as cities (where direct <span class="inline-formula">CO₂</span> emissions related to fossil fuel combustion in transport, residential, commercial sectors, etc., excluding emissions from electricity-producing power plants, occur), isolated power plants, and manufacturing facilities, which cover a small fraction of the land surface. The coverage of all high-emitting cities and point sources across the globe by bottom-up inventories is far from complete, and for most of those covered, the uncertainties in <span class="inline-formula">CO₂</span> emission estimates in bottom-up inventories are too large to allow continuous and rigorous assessment of emission changes (Gurney et al., 2019). Space-borne imagery of atmospheric <span class="inline-formula">CO₂</span> has the potential to provide independent estimates of <span class="inline-formula">CO₂</span> emissions from hotspots. But first, what a hotspot is needs to be defined for the purpose of satellite observations. The proposed space-borne imagers with global coverage planned for the coming decade have a pixel size on the order of a few square kilometers and a <span class="inline-formula">XCO₂</span> accuracy and precision of <span class="inline-formula">&lt;1</span>&thinsp;ppm for individual measurements of vertically integrated columns of dry-air mole fractions of <span class="inline-formula">CO₂</span> (<span class="inline-formula">XCO₂</span>). This resolution and precision is insufficient to provide a cartography of emissions for each individual pixel. Rather, the integrated emission of diffuse emitting areas and intense point sources is sought. In this study, we characterize area and point fossil fuel <span class="inline-formula">CO₂</span> emitting sources which generate coherent <span class="inline-formula">XCO₂</span> plumes that may be observed from space. We characterize these emitting sources around the globe and they are referred to as “emission clumps” hereafter. An algorithm is proposed to identify emission clumps worldwide, based on the ODIAC global high-resolution 1&thinsp;km fossil fuel emission data product. The clump algorithm selects the major urban areas from a GIS (geographic information system) file and two emission thresholds. The selected urban areas and a high emission threshold are used to identify clump cores such as inner city areas or large power plants. A low threshold and a random walker (RW) scheme are then used to aggregate all grid cells contiguous to cores in order to define a single clump. With our definition of the thresholds, which are appropriate for a space imagery with 0.5&thinsp;ppm precision for a single <span class="inline-formula">XCO₂</span> measurement, a total of 11&thinsp;314 individual clumps, with<span id="page688"/> 5088 area clumps, and 6226 point-source clumps (power plants) are identified. These clumps contribute 72&thinsp;% of the global fossil fuel <span class="inline-formula">CO₂</span> emissions according to the ODIAC inventory. The emission clumps is a new tool for comparing fossil fuel <span class="inline-formula">CO₂</span> emissions from different inventories and objectively identifying emitting areas that have a potential to be detected by future global satellite imagery of <span class="inline-formula">XCO₂</span>. The emission clump data product is distributed from <a href="https://doi.org/10.6084/m9.figshare.7217726.v1">https://doi.org/10.6084/m9.figshare.7217726.v1</a>.</p>