the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Jan 2026
Quantifying and Attributing CO Emissions over Central Asia using TROPOMI and Explicit Observational Uncertainty
Abstract. Carbon monoxide (CO) is a crucial atmospheric constituent influencing both air quality and climate. Using TROPOMI CO and HCHO column retrievals within the Model-Free Inversion Estimation Framework (MFIEF), this study quantified daily, gridded CO emissions in Central Asia (Xinjiang-China, Kazakhstan, Kyrgyzstan, and Uzbekistan) for 2019–2024. Results reveal a marked interannual decline of ~ 38 % in mean emissions, accompanied by a weakening of emission hotspots. Seasonal peaks in winter and early spring highlight the roles of heating and industrial demand. Importantly, explicit perturbation-based uncertainty analysis showed that ~ 69 % of grid-level estimates are unreliable if observational uncertainties are ignored or using an overly simplified emissions estimation approach, underscoring the nonlinear propagation of retrieval errors. By integrating coal consumption data, we confirm the consistency between satellite-inferred emissions and bottom-up activity estimates, while also identifying missing sources such as underground coal fires. This study demonstrates the effectiveness of MFIEF in data-scarce regions, provides actionable insights for inventory improvement and mitigation strategies, and highlights the framework's potential extension to CH4 and CO2 retrieval-based emission estimation.
Competing interests: Jason Blake Cohen is a member of the editorial board of Atmospheric Chemistry and Physics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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RC1: 'Comment on egusphere-2025-5890', Anonymous Referee #1, 03 Jul 2026
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AC1: 'Reply on RC1', Ye Feng, 01 Oct 2026
We sincerely thank the reviewer for the careful evaluation of our manuscript and for the constructive and insightful comments. We greatly appreciate the time and effort devoted to reviewing our work. The comments have helped us improve both the scientific presentation and the clarity of the manuscript. We have carefully considered all suggestions and revised the manuscript accordingly. In this response, your original comments are completely unedited and are given in yellow highlight, our responses are given in blue text and updates to the paper are given in purple text.
The revisions include: (1) clarifying the potential influence of biomass burning and residential solid-fuel combustion; (2) distinguishing the study domain from the facilities used in the source-category analysis; (3) clarifying the propagation of observational uncertainty into CO emission estimates and distinguishing this contribution from total emission uncertainty; (4) moderating claims regarding independent validation, EDGAR bias, policy effectiveness, and coal-fire seasonality; (5) adding a seasonally adjusted trend analysis with HAC standard errors and a seasonal Mann-Kendall robustness test; (6) quantifying the 37.9% endpoint decline and the 40.8% reduction in hotspot intensity; and (7) revising the text, captions, terminology, and statistical interpretation throughout the manuscript.
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AC1: 'Reply on RC1', Ye Feng, 01 Oct 2026
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RC2: 'Comment on egusphere-2025-5890', Anonymous Referee #2, 20 Aug 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2025-5890/egusphere-2025-5890-RC2-supplement.pdf
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AC2: 'Reply on RC2', Ye Feng, 01 Oct 2026
We sincerely thank the reviewer for the careful evaluation of our manuscript and for the constructive and insightful comments. We greatly appreciate the time and effort devoted to reviewing our work. The comments have helped us improve both the scientific presentation and the clarity of the manuscript. We have carefully considered all suggestions and revised the manuscript accordingly. In this response, your original comments are completely unedited and are given in yellow highlight, our responses are given in blue text and updates to the paper are given in purple text.
Following these comments, we have revised the manuscript. The major changes include: (1) clarifying that the comparison with EDGAR and coal-consumption data provides contextual and physical consistency checks rather than independent validation of the MFIEF inversion; (2) expanding the discussion of the limitations of the inversion in the absence of independent ground-based CO emission measurements; (3) quantitatively characterizing the interannual decline and weakening of emission hotspots; (4) clarifying the nature of the Wugonggou underground coal fire and separating its temporal behavior from interpretations associated with anthropogenic emission-control policies; (5) clarifying the definition and purpose of the valid-observation metric in Fig. 7; (6) highlighting the relationship between power-plant coal consumption and the derived emission factors; and (7) comprehensively revising the figures, captions, labels, terminology, and language throughout the manuscript.
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AC2: 'Reply on RC2', Ye Feng, 01 Oct 2026
Status: closed
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RC1: 'Comment on egusphere-2025-5890', Anonymous Referee #1, 03 Jul 2026
General comments:
This study quantified daily gridded CO emissions in Central Asia for 2019-2024 and assessed CO trends and hotspots. This study provided actionable insights for inventory improvement and migration strategies. This topic is interesting and meaningful to readers. I only have some small suggestions.
Special comments:
- Lines 35-37. CO is also emitted by biomass burning. What about biomass burning emissions in the research region? For example, anthropogenic biomass burning for cooking and heating from wood and yak dung in rural areas.
- Figure 1. Strangely, there are no power/steel plants or coal bases in the Central Asian countries. I also suggest adding the province or country names in Figure 1; otherwise, readers may be confused by the regions mentioned in the text.
- Line 195-200. Equation 2 was used to calculate the change in CO emissions. But uncertainty is usually not defined as the change of certain values.
- Figure 4A. Why coal fire also show a clear seasonal variation in CO emissions?
- Figure 8. It is easy to imagine the CO emission unit in coal fire and urban centers as they are area sources. But for power plants, which are point sources, how do we calculate the emission? Or using the pixel data for the power plant location?
- Table 1. Many cities, coal-fired sites, steel plants, and power plants are shown in Figure 1. So the data summarized in Table 1 are calculated from 1 typical site or averages of all the same types of locations?
- Typo errors: please check the text again during revision. Some are listed below.
- Line 82: In addition to Kazakhstan, Kyrgyzstan, and Uzbekistan, some parts of other countries like Tajikistan, Afghanistan, and Pakistan are also shown in Figure 1.
- two “and then resampled” in line 100.
- Line 147. (Li et al., 2025) to Li et al., (2025)
- Use Figure or Fig. in the manuscript, not all of them.
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AC1: 'Reply on RC1', Ye Feng, 01 Oct 2026
We sincerely thank the reviewer for the careful evaluation of our manuscript and for the constructive and insightful comments. We greatly appreciate the time and effort devoted to reviewing our work. The comments have helped us improve both the scientific presentation and the clarity of the manuscript. We have carefully considered all suggestions and revised the manuscript accordingly. In this response, your original comments are completely unedited and are given in yellow highlight, our responses are given in blue text and updates to the paper are given in purple text.
The revisions include: (1) clarifying the potential influence of biomass burning and residential solid-fuel combustion; (2) distinguishing the study domain from the facilities used in the source-category analysis; (3) clarifying the propagation of observational uncertainty into CO emission estimates and distinguishing this contribution from total emission uncertainty; (4) moderating claims regarding independent validation, EDGAR bias, policy effectiveness, and coal-fire seasonality; (5) adding a seasonally adjusted trend analysis with HAC standard errors and a seasonal Mann-Kendall robustness test; (6) quantifying the 37.9% endpoint decline and the 40.8% reduction in hotspot intensity; and (7) revising the text, captions, terminology, and statistical interpretation throughout the manuscript.
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RC2: 'Comment on egusphere-2025-5890', Anonymous Referee #2, 20 Aug 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2025-5890/egusphere-2025-5890-RC2-supplement.pdf
-
AC2: 'Reply on RC2', Ye Feng, 01 Oct 2026
We sincerely thank the reviewer for the careful evaluation of our manuscript and for the constructive and insightful comments. We greatly appreciate the time and effort devoted to reviewing our work. The comments have helped us improve both the scientific presentation and the clarity of the manuscript. We have carefully considered all suggestions and revised the manuscript accordingly. In this response, your original comments are completely unedited and are given in yellow highlight, our responses are given in blue text and updates to the paper are given in purple text.
Following these comments, we have revised the manuscript. The major changes include: (1) clarifying that the comparison with EDGAR and coal-consumption data provides contextual and physical consistency checks rather than independent validation of the MFIEF inversion; (2) expanding the discussion of the limitations of the inversion in the absence of independent ground-based CO emission measurements; (3) quantitatively characterizing the interannual decline and weakening of emission hotspots; (4) clarifying the nature of the Wugonggou underground coal fire and separating its temporal behavior from interpretations associated with anthropogenic emission-control policies; (5) clarifying the definition and purpose of the valid-observation metric in Fig. 7; (6) highlighting the relationship between power-plant coal consumption and the derived emission factors; and (7) comprehensively revising the figures, captions, labels, terminology, and language throughout the manuscript.
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AC2: 'Reply on RC2', Ye Feng, 01 Oct 2026
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General comments:
This study quantified daily gridded CO emissions in Central Asia for 2019-2024 and assessed CO trends and hotspots. This study provided actionable insights for inventory improvement and migration strategies. This topic is interesting and meaningful to readers. I only have some small suggestions.
Special comments: