Carbon dioxide (CO₂) has been recognized as the most important anthropogenic greenhouse gas owing to its significant impact on global warming and climate change.

The United Nations Climate Change Conference (24th Conference of the Parties, COP24) will conduct a climate change action global stock-take for each of five years starting in 2023. Therefore, we need a new method to verify how much human emissions impact the global carbon cycle and climate change.

The 1st Chinese Carbon Dioxide Monitoring Satellite Mission, known as TanSat, was launched in December 2016 to monitor CO₂ concentrations in the atmosphere over the globe. The 1st TanSat global map of CO₂ dry-air mixing ratio (XCO₂) measurements over land was released as a version-1 data product with an accuracy of 2.11 parts per million by volume (ppmv).

"Unfortunately, it is not accurate enough to support estimation of anthropogenic CO₂ emissions in cities because it has a 1-1.5 ppm gradient across urban areas," said YANG Dongxu, a scientist with the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences (CAS), who is closely involved in TanSat data retrieval. "On TanSat's 4th birthday coming this year, we will introduce a new version [version 2] of the TanSat global XCO₂ product."

The new TanSat global XCO₂ product is retrieved by the Institute of Atmospheric Physics Carbon dioxide retrieval Algorithm for Satellite remote sensing (IAPCAS), and the European Space Agency (ESA) Climate Change Initiative plus (CCI+) TanSat XCO2 product by University of Leicester Full Physics (UoL-FP) retrieval algorithm. 

The TanSat v2 XCO₂ data product can be obtained from the CASA (the Cooperation on the Analysis of carbon SAtellites data) TanSat data and science service (www.chinageoss.org/tansat).

Intercomparison of TanSat XCO₂ retrieval between the two algorithms shows good agreement for global Total Column Carbon Observing Network (TCCON) overpass measurements with 34,699 individual measurements. The dispersion between the two data products has a standard deviation of 1.28 ppmv, and there is also a -0.35 ppmv overall bias between both. These intercomparison results are introduced in a recently published paper in Advances in Atmospheric Sciences.

In January 2020, a protocol was signed between the National Remote Sensing Center of the China Ministry of Science and Technology of China (MOST/NRSCC) and ESA regarding the intended coordination of their activities in the Remote Sensing of Greenhouse Gases and Related Missions. MOST/NRSCC and ESA intend TanSat to be a third-party mission of ESA, and TanSat data have been included in key ESA programs such as the Climate Change Initiative plus (CCI+) and Earthnet Data Assessment Pilot (EDAP).

The new dataset will be involved in global carbon flux estimations and climate studies in the near future. The TanSat mission will never stop, and developments are required in future generations of TanSat missions to contribute further to global stock-take and carbon-neutral research.