نبذة مختصرة : We assess the theoretical capability of the upcoming France–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 cloud 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 by virtue of its wider scan area that typically yields more cloud-free observations, can retrieve the total emissions of the truth within 7 % over Paris and 21 % over London. 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 reduce bias in estimating 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.
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