08 Sep 2022
08 Sep 2022
Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).

Theoretical assessment of the ability of the MicroCarb satellite city-scan observing mode to estimate urban CO2 emissions

Kai Wu1, Paul I. Palmer1,2, Dien Wu3, Denis Jouglet4, Liang Feng1,2, and Tom Oda5,6,7 Kai Wu et al.
  • 1School of GeoSciences, University of Edinburgh, Edinburgh, UK
  • 2National Centre for Earth Observation, University of Edinburgh, Edinburgh, UK
  • 3Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
  • 4Centre National d’Etudes Spatiales, Toulouse, France
  • 5Earth from Space Institute, Universities Space Research Association, Columbia, MD, USA
  • 6Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD, USA
  • 7Graduate School of Engineering, Osaka University, Suita, Osaka, Japan

Abstract. We assess the theoretical capability of the upcoming French-UK MicroCarb satellite, which has a city-scan observing mode, to determine integrated urban emissions of carbon dioxide (CO2). To achieve this we report results from a series of closed-loop numerical experiments that use an atmospheric transport model with anthropogenic and biogenic fluxes to determine the corresponding changes in atmospheric CO2 column, accounting for changes in measurement coverage due to clouds loading. We use a Maximum A Posteriori inverse method to infer the CO2 fluxes based on the measurements and the a priori information. Using an urban CO2 inversion system, we explore the relative performance of alternative two-sweep and three-sweep city observing strategies to quantify CO2 emissions over the cities of Paris and London in different months when biospheric fluxes vary in magnitude. We find that both the two-sweep and three-sweep observing modes are able to reduce a priori flux errors by 20–40 % over Paris and London. The three-sweep observing strategy, which generally outperforms the two-sweep mode, can retrieve the total emissions of the truth within 7 % over Paris and 21 % over London, by virtue of its wider scan area that typically yields more cloud-free scenes. The performance of the limited-domain city-mode observing strategies is sensitive to cloud coverage and particularly sensitive to the prevailing wind direction. We also find that seasonal photosynthetic uptake of CO2 by the urban biosphere weakens atmospheric CO2 gradients across both cities thereby reducing the sensitivity of urban CO2 enhancements and subsequently compromising the ability of MicroCarb to estimate urban CO2 emissions. This suggests that additional trace gases co-emitted with anthropogenic CO2 emissions, but unaffected by the land biosphere, are needed to quantify sub-city scale CO2 emissions during months when the urban biosphere is particularly active.

Kai Wu et al.

Status: open (until 14 Oct 2022)

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Kai Wu et al.

Kai Wu et al.


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Short summary
We evaluate the theoretical ability of the upcoming MicroCarb satellite to estimate urban CO2 emissions over Paris and London. We explore the relative performance of alternative two-sweep and three-sweep city observing modes and take into account the impacts of cloud cover and urban biological CO2 fluxes. Our results find both the two-sweep and three-sweep observing modes are able to reduce prior flux errors by 20–40 % depending on the prevailing wind direction and cloud coverage.