Since CO₂ has been recognized as the most important anthropogenic greenhouse gas owing to its significant impact on global warming and climate change, there have been a substantial number of studies that have focused on investigating the status of CO₂ in the atmosphere in the past and present, and how it will change in the future.

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, in support of these efforts, 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, which was supported by the Ministry of Science and Technology of China, the Chinese Academy of Sciences, and the China Meteorological Administration, launched in December 2016 for the purpose of monitoring 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 ppmv (parts per million by volume).

"Unfortunately, it is not accurate enough to support estimation of anthropogenic CO₂ emissions in cities due to it having a 1–1.5 ppm gradient across urban areas, as shown from ground-based measurement in Paris," explains YANG Dongxu, a scientist with the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP/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 IAPCAS (the Institute of Atmospheric Physics Carbon Dioxide Retrieval Algorithm for Satellite Remote Sensing), and the European Space Agency (ESA) Climate Change Initiative plus (CCI+) TanSat XCO₂ product is retrieved by the University of Leicester Full Physics (UoL-FP) retrieval algorithm. The new TanSat XCO₂ data product is now retrieved by IAP/CAS using the O₂ A-band and CO₂ weak band together, after a new approach has been developed to improve the retrieval accuracy by optimizing the TanSat measured spectrum. 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.

Citation: Yang, D., and Coauthors, 2021: A new TanSat XCO₂ global product towards climate studies. Adv. Atmos. Sci., https://doi.org/10.1007/s00376-020-0297-y.

Media contact: Ms. LIN Zhenng, jennylin@mail.iap.ac.cn