Derivation of Emissions From Satellite-Observed Column Amounts and Its Application to TROPOMI NO₂ and CO Observations

A unified framework that connects emissions with satellite-observed column amounts is derived from first principles. The emission information originates from the inner product of the horizontal wind and the gradient of column amount, which is more accurate than the horizontal flux divergence as used in previous studies. Additionally, the topographical and chemical effects are accounted for through fitted scale height and chemical lifetime. This framework is applied to derive NO_x and CO emissions over the CONUS from TROPOspheric Monitoring Instrument NO₂ and CO observations. High-resolution (0.04°) emission mapping over the CONUS reveals unprecedented details, including CO emissions in major cities and NO_x emissions from large cities, power plants, and major roadways. Monthly resolved NO_x emissions show decrease and rebound after the COVID-19 pandemic. This framework is integrated with the physical oversampling algorithm and can be readily applied to other products from the new-generation satellite instruments.