Toward monitoring daily anthropogenic CO2 emissions with air pollution sensors from space

Real-time global monitoring of CO2 emissions via satellites would be valuable for climate mitigation. While CO2 emissions may be inferred from measurements of co-emitted nitrogen oxide pollutants that are more easily detected from space, this method remains insufficiently tested during normal, non-pandemic emission patterns. Here, we integrate satellite NO2 data, a detailed emission inventory, and atmospheric modeling to infer China's daily NOx emissions for 2020 and 2021, subsequently estimating CO2 emissions with optimized CO2-to-NOx emission ratios. Our results illustrate increased CO2 but decreased NOx emissions in China from 2020 to 2021, with substantial daily variations shaped by socioeconomic dynamics including economic rebound and weakened industry production. Our NOx inversion-based CO2 emission estimates agree with fuel consumption better than a frequently updated emission inventory using incomplete activity data, a commonly used approach to monitor emissions. With remote sensing technology advancing, our approach offers a prototype for real-time daily anthropogenic emission tracking.