Evaluating the performance of carbon dioxide and methane observations from carbon-monitoring satellite products over China.

As the primary greenhouse gases contributing to climate change, carbon dioxide (CO₂) and methane (CH) play a critical role in the Earth's radiative balance and temperature regulation. Continuous and accurate satellite monitoring of CO₂ and CH₄ is essential for developing effective policies and strategies to mitigate their impacts. This study utilizes ground-based Fourier-transform infrared measurements from the Total Carbon Column Observing Network (TCCON) to evaluate the performance of current mainstream carbon-monitoring satellites over China, the world's largest carbon emitter. Our findings show that TanSat performs excellently for CO₂ observations at both Hefei and Xianghe sites, achieving a standard deviation (SD) of about 2 ppm and a maximum bias of 0.25 ppm, dropping to 0.02 ppm at Xianghe. In contrast, Orbiting Carbon Observatory (OCO)-3 and Greenhouse Gases Observing Satellite (GOSAT)-2 CO measurements are slightly less reliable. For CH₄ monitoring, GOSAT outperforms GOSAT-2, with a SD of around 14 ppb and bias within 2 ppb, compared to GOSAT-2's 17.58 ppb SD and 2.15 ppb bias at Hefei. These results indicate that the latest carbon-monitoring satellites are less precise and accurate than their predecessors. Additionally, we provide detailed assessments of the data products based on different spatial matching criteria. We also discuss the variation in satellite accuracy over time, revealing periodic bias variations and the instability in satellite performance. Furthermore, while the spatial distribution trends of satellite acquisitions are generally consistent on an annual scale, we observe non-negligible differences in the annual averages across specific land surfaces. Our study presents a meticulous evaluation of the reliability of satellite-based carbon-monitoring products over the Chinese region and provides scientific evidence for analyzing uncertainty in carbon source-sink studies.