The Copernicus Anthropogenic CO₂ Monitoring (CO2M) mission is a proposed constellation of imaging satellites with a CO₂ instrument as main payload and optionally instruments for NO₂, CO and aerosols. This study demonstrates the huge benefit of an NO₂ instrument for detecting city plumes and weak point sources. Its main advantages are the higher signal-to-noise ratio and the lower sensitivity to clouds that significantly increases the number of observations available for quantifying CO₂ emission.