Enhanced Quantification of Global Carbon Emitters Using Collocated OCO‐3 CO ₂ and NO ₂ Observations From Twin Polar‐Orbiting Satellites

Abstract Satellite‐based estimates of fossil fuel carbon dioxide (FFCO 2 ) emissions are crucial for global stocktaking but are limited by sparse coverage. As nitrogen dioxide (NO 2 ) observations can enhance CO 2 emission estimates, we use NO 2 observations from twin polar‐orbiting satellites (GaoFen‐5B and DaQi‐1) to constrain carbon emission estimates based on the OCO‐3 XCO 2 measurements. Compared previous CO 2 estimation constrained by polar‐orbiting satellites (e.g., Tropospheric Monitoring Instrument), this approach detects 40% more daily emission cases and reduces uncertainties by up to 12%, primarily due to reduced temporal differences and increased observation frequency. The improved estimates cover 69 global emission cases, mainly in East Asia, Europe, the Middle East, and North America. About 45% of the estimated emissions are lower than bottom‐up inventory values, potentially reflecting the impact of local emission control efforts. These findings highlight the importance of satellite monitoring for FFCO 2 emissions and the value of future missions with high‐resolution collocated NO 2 /CO 2 measurements.