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Passive remote sensing of atmospheric carbon dioxide uses spectroscopic measurements of sunlight backscattered by the Earth's surface and atmosphere. The current state-of-the-art retrieval methods use three different spectral bands, the oxygen A band at 0.76 µ m and the weak and strong CO2 absorption bands at 1.61 and 2.06 µ m, respectively, to infer information on light scattering and the carbon dioxide column-averaged dry-air mole fraction XCO2. In this study, we propose a one-band XCO2 retrieval technique which uses only the 2.06 µ m band measurements from the Orbiting Carbon Observatory-2 (OCO-2) satellite. We examine the data quality by comparing the OCO-2 XCO2 with collocated ground-based measurements from the Total Carbon Column Observing Network (TCCON). Over land and ocean the OCO-2 one-band retrieval shows differences from TCCON observations with a standard deviation of ∼1.30 ppm and a station-to-station variability of ∼0.50 ppm. Moreover, we compare one-band and three-band retrievals over Europe, the Middle East, and Africa and see high correlation between the two retrievals with a SD of 0.93 ppm. Compared to the three-band retrievals, XCO2 retrievals using only the 2.06 µ m band have similar retrieval accuracy, precision, and data yield. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic resulted in reduced anthropogenic carbon dioxide (CO 2) emissions during 2020 in large parts of the world. To investigate whether a regional-scale reduction of anthropogenic CO 2 emissions during the COVID-19 pandemic can be detected using space-based observations of atmospheric CO 2 , we have analysed a small ensemble of OCO-2 and GOSAT satellite retrievals of column-averaged dry-air mole fractions of CO 2 , i.e. XCO 2. We focus on East China and use a simple data-driven analysis method. We present estimates of the relative change of East China monthly emissions in 2020 relative to previous periods, limiting the analysis to October-to-May periods to minimize the impact of biogenic CO 2 fluxes. The ensemble mean indicates an emission reduction by approximately 10 % ± 10 % in March and April 2020. However, our results show considerable month-to-month variability and significant differences across the ensemble of satellite data products analysed. For example, OCO-2 suggests a much smaller reduction (∼ 1 %–2 % ± 2 %). This indicates that it is challenging to reliably detect and to accurately quantify the emission reduction with current satellite data sets. There are several reasons for this, including the sparseness of the satellite data but also the weak signal; the expected regional XCO 2 reduction is only on the order of 0.1–0.2 ppm. Inferring COVID-19-related information on regional-scale CO 2 emissions using current satellite XCO 2 retrievals likely requires, if at all possible, a more sophisticated analysis method including detailed transport modelling and considering a priori information on anthropogenic and natural CO 2 surface fluxes. [ABSTRACT FROM AUTHOR]

Previously, satellite-derived atmospheric carbon dioxide (CO2) and methane (CH4) Essential Climate Variable (ECV) data sets have been generated and made available via the GHG-CCI project of ESA's Climate Change Initiative (CCI, http://www.esa-ghg-cci.org/). Currently, the production and provision of these data sets is being continued operationally via the Copernicus Climate Change Service (C3S, https://climate.copernicus.eu/), which is implemented by ECMWF on behalf of the European Commission (EC). In this presentation an overview about these data sets will be given focusing on column-averaged dry-air mole fractions of CO2, denoted XCO2. Currently, this C3S data set covers the time period 2003-2017 but will be extended each year but one additional year. In addition, XCO2 from GOSAT is generated in quasi near-real-time for the Copernicus Atmosphere Monitoring Service (CAMS, https://atmosphere.copernicus.eu/) and the combined C3S/CAMS data set covering 2003-2018 has been used to provide up-to-date information on, for example, annual mean XCO2 growth rates. Main applications for the C3S data set are climate and carbon related applications such as comparisons with climate models and improving our knowledge of CO2 sources and sinks. Current satellites have however not been optimized to monitor anthropogenic emissions. To improve this situation in the future, ESA and the EC supported by other institutions and European and international scientist are working on the specification of a CO2 Monitoring (CO2M) mission, which will likely be a constellation of Sentinel satellites. In addition to high-resolution (approx. 2x2 km2) CO2 and CH4 observations, CO2M will also provide Solar-Induced-Fluorescence (SIF) and information on NO2 and aerosols probably via dedicated instruments on the same platform. In the presentation an overview about these current and future Copernicus CO2-related activities will be presented. [ABSTRACT FROM AUTHOR]