Improving XCO2 retrieval under high aerosol loads with fused satellite aerosol Data: Advancing understanding of anthropogenic emissions

Satellite measurements of the column-averaged dry air mole fraction of carbon dioxide (XCO₂) have been successfully employed to quantify anthropogenic carbon emissions under clean atmospheric conditions. However, for some large anthropogenic sources such as megacities or coal-fired power plants, which are often accompanied by high aerosol loads, especially in developing countries, atmospheric XCO₂ retrieval remains challenging. Traditional XCO₂ retrieval algorithms typically rely on model-based or single-satellite aerosol information as constraints, which offer limited accuracy under high aerosol conditions, resulting in imperfect aerosol scattering characterization. Various satellite sensors dedicated to aerosol detection provide distinct aerosol products, each with its strengths. The fusion of these products offers the potential for more accurate scattering characterization in high aerosol scenarios. Therefore, in this study, we first fused four satellite aerosol products from MODIS and VIIRS sensors using the Bayesian maximum entropy method and then incorporated it into the XCO₂ retrieval from NASA OCO-2 observations to improve retrieval quality under high aerosol conditions. Compared to the operational products, we find that XCO₂ retrievals coupled with co-located fused aerosol data exhibit improved accuracy and precision at higher aerosol loads, against the Total Carbon Column Observing Network (TCCON). Specifically, for high aerosol loadings (AOD@755 nm > 0.25), the mean bias and mean absolute error (MAE) of the XCO₂ retrieval are reduced by 0.14 ppm and 0.1 ppm, respectively, while the standard deviation of the XCO₂ error reaches 1.68 ppm. The detection capability of point source CO₂ emissions corresponding to this precision (1.68 ppm) is also evaluated in this study. Results show that the number of detectable coal-fired power plants globally under high aerosol conditions can be increased by 39 % compared to the application of operational products. These results indicate that using fused satellite aerosol products effectively improves XCO₂ retrieval under high aerosol conditions, advancing carbon emission understanding from important anthropogenic sources, particularly in developing countries.