29 Apr 2022
29 Apr 2022
Status: this preprint is currently under review for the journal ACP.

Methane emissions from China: a high-resolution inversion of TROPOMI satellite observations

Zichong Chen1, Daniel Jacob1, Hannah Nesser1, Melissa Sulprizio1, Alba Lorente2, Daniel Varon1, Xiao Lu3, Lu Shen4, Zhen Qu1, Elise Penn1, and Xueying Yu5 Zichong Chen et al.
  • 1Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
  • 2SRON Netherlands Institute for Space Research, Leiden, the Netherlands
  • 3School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, Guangdong, China
  • 4Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China
  • 5Department of Soil, Water, and Climate, University of Minnesota, Saint Paul, MN, USA

Abstract. We quantify methane emissions in China and the contributions from different sectors by inverse analysis of 2019 TROPOMI satellite observations of atmospheric methane. The inversion uses as prior estimate the national sector-resolved anthropogenic emission inventory reported by the Chinese government to the United Nations Framework Convention on Climate Change (UNFCCC) and thus serves as a direct evaluation of that inventory. Emissions are optimized with a Gaussian mixture model (GMM) at up to 0.25° × 0.3125° resolution. The optimization is done analytically assuming lognormally distributed errors on prior emissions. Errors and information content on the optimal estimates are obtained directly from the analytical solution and also through a 36-member inversion ensemble. Our optimal estimate for total anthropogenic emissions in China is 65.0 (57.7–68.4) Tg a-1, where parentheses indicate uncertainty range. Contributions from individual sectors include 16.6 (15.6–17.6) Tg a-1 for coal, 2.3 (1.8–2.5) for oil, 0.29 (0.23–0.32) for gas, 17.8 (15.1–21.0) for livestock, 9.3 (8.2–9.9) for waste, 11.9 (10.7–12.7) for rice paddies, and 6.7 (5.8–7.1) for other sources. Our estimate is 21 % higher than the Chinese inventory reported to the UNFCCC (53.6 Tg a-1), reflecting upward corrections to emissions from oil (+147 %), gas (+61 %), livestock (+37 %), waste (+41 %), and rice paddies (+34 %), but downward correction for coal (-15 %). It is also higher than previous inverse studies (43–62 Tg a-1) that used the much sparser GOSAT satellite observations and were conducted at coarser resolution. We are in particular better able to separate coal and rice emissions. Our higher livestock emissions are attributed largely to northern China where GOSAT has little sensitivity. Our higher waste emissions reflect at least in part a rapid growth in wastewater treatment in China. Underestimate of oil emissions in the UNFCCC report appears to reflect unaccounted super-emitting facilities. Gas emissions in China are mostly from distribution, in part because of low emission factors from production and in part because 42 % of the gas is imported. Our estimate of emissions per unit of domestic gas production indicates a low life-cycle loss rate of 1.7 (1.3–1.9) %, which would imply net climate benefits from the current coal-to-gas energy transition in China. However, this small loss rate is somewhat misleading considering China’s high gas imports, including from Turkmenistan where emission per unit of gas production is very high.

Zichong Chen et al.

Status: open (until 10 Jun 2022)

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Zichong Chen et al.

Zichong Chen et al.


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Short summary
We quantify methane emissions in China and contributions from different sectors by inverse analysis of 2019 TROPOMI satellite observations of atmospheric methane. We find that anthropogenic methane emissions for China are underestimated in the national inventory. Our estimate of emissions indicates a small life-cycle loss rate, implying net climate benefits from the current ‘coal-to-gas’ energy transition in China. However, this small loss rate can be misleading given China’s high gas imports.