My research interests include atmospheric chemistry, greenhouse gas emissions, satellite remote sensing retrievals, and carbon mitigation. I use inverse modeling and other data-driven approaches to address the above issues across multiple scales, in particular, to quantify methane emissions from point source level to the global budget.

Stanford Advisors

All Publications

  • Estimation of Anthropogenic CH4 and CO2 Emissions in Taiyuan-Jinzhong Region: One of the World's Largest Emission Hotspots JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Hu, C., Xiao, W., Griffis, T. J., Xiao, Q., Wang, S., Zhang, Y., Wang, W., Zhu, L., Chen, X., Yu, X., Lee, X. 2023; 128 (8)
  • A high-resolution satellite-based map of global methane emissions reveals missing wetland, fossil fuel, and monsoon sources ATMOSPHERIC CHEMISTRY AND PHYSICS Yu, X., Millet, D. B., Henze, D. K., Turner, A. J., Delgado, A., Bloom, A., Sheng, J. 2023; 23 (5): 3325-3346
  • Methane emissions from China: a high-resolution inversion of TROPOMI satellite observations ATMOSPHERIC CHEMISTRY AND PHYSICS Chen, Z., Jacob, D. J., Nesser, H., Sulprizio, M. P., Lorente, A., Varon, D. J., Lu, X., Shen, L., Qu, Z., Penn, E., Yu, X. 2022; 22 (16): 10809-10826
  • How well can inverse analyses of high-resolution satellite data resolve heterogeneous methane fluxes? Observing system simulation experiments with the GEOS-Chem adjoint model (v35) GEOSCIENTIFIC MODEL DEVELOPMENT Yu, X., Millet, D. B., Henze, D. K. 2021; 14 (12): 7775-7793
  • Fossil Versus Nonfossil CO Sources in the US: New Airborne Constraints From ACT-America and GEM GEOPHYSICAL RESEARCH LETTERS Gonzalez, A., Millet, D. B., Yu, X., Wells, K. C., Griffis, T. J., Baier, B. C., Campbell, P. C., Choi, Y., DiGangi, J. P., Gvakharia, A., Halliday, H. S., Kort, E. A., McKain, K., Nowak, J. B., Plant, G. 2021; 48 (11)
  • A Multiyear Constraint on Ammonia Emissions and Deposition Within the US Corn Belt GEOPHYSICAL RESEARCH LETTERS Hu, C., Griffis, T. J., Frie, A., Baker, J. M., Wood, J. D., Millet, D. B., Yu, Z., Yu, X., Czarnetzki, A. C. 2021; 48 (6)
  • Aircraft-based inversions quantify the importance of wetlands and livestock for Upper Midwest methane emissions ATMOSPHERIC CHEMISTRY AND PHYSICS Yu, X., Millet, D. B., Wells, K. C., Henze, D. K., Cao, H., Griffis, T. J., Kort, E. A., Plant, G., Deventer, M. J., Kolka, R. K., Roman, D., Davis, K. J., Desai, A. R., Baier, B. C., McKain, K., Czarnetzki, A. C., Bloom, A. 2021; 21 (2): 951-971


    We apply airborne measurements across three seasons (summer, winter and spring 2017-2018) in a multi-inversion framework to quantify methane emissions from the US Corn Belt and Upper Midwest, a key agricultural and wetland source region. Combing our seasonal results with prior fall values we find that wetlands are the largest regional methane source (32 %, 20 [16-23] Gg/d), while livestock (enteric/manure; 25 %, 15 [14-17] Gg/d) are the largest anthropogenic source. Natural gas/petroleum, waste/landfills, and coal mines collectively make up the remainder. Optimized fluxes improve model agreement with independent datasets within and beyond the study timeframe. Inversions reveal coherent and seasonally dependent spatial errors in the WetCHARTs ensemble mean wetland emissions, with an underestimate for the Prairie Pothole region but an overestimate for Great Lakes coastal wetlands. Wetland extent and emission temperature dependence have the largest influence on prediction accuracy; better representation of coupled soil temperature-hydrology effects is therefore needed. Our optimized regional livestock emissions agree well with the Gridded EPA estimates during spring (to within 7 %) but are ∼25 % higher during summer and winter. Spatial analysis further shows good top-down and bottom-up agreement for beef facilities (with mainly enteric emissions) but larger (∼30 %) seasonal discrepancies for dairies and hog farms (with >40 % manure emissions). Findings thus support bottom-up enteric emission estimates but suggest errors for manure; we propose that the latter reflects inadequate treatment of management factors including field application. Overall, our results confirm the importance of intensive animal agriculture for regional methane emissions, implying substantial mitigation opportunities through improved management.

    View details for DOI 10.5194/acp-21-951-2021

    View details for Web of Science ID 000613269200002

    View details for PubMedID 33613665

    View details for PubMedCentralID PMC7894053

  • Top-Down Constraints on Methane Point Source Emissions From Animal Agriculture and Waste Based on New Airborne Measurements in the US Upper Midwest JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES Yu, X., Millet, D. B., Wells, K. C., Griffis, T. J., Chen, X., Baker, J. M., Conley, S. A., Smith, M. L., Gvakharia, A., Kort, E. A., Plant, G., Wood, J. D. 2020; 125 (1)


    Agriculture and waste are thought to account for half or more of the U.S. anthropogenic methane source. However, current bottom-up inventories contain inherent uncertainties from extrapolating limited in situ measurements to larger scales. Here, we employ new airborne methane measurements over the U.S. Corn Belt and Upper Midwest, among the most intensive agricultural regions in the world, to quantify emissions from an array of key agriculture and waste point sources. Nine of the largest concentrated animal feeding operations in the region and two sugar processing plants were measured, with multiple revisits during summer (August 2017), winter (January 2018), and spring (May-June 2018). We compare the top-down fluxes with state-of-science bottom-up estimates informed by U.S. Environmental Protection Agency methodology and site-level animal population and management practices. Top-down point source emissions are consistent with bottom-up estimates for beef concentrated animal feeding operations but moderately lower for dairies (by 37% on average) and significantly lower for sugar plants (by 80% on average). Swine facility results are more variable. The assumed bottom-up seasonality for manure methane emissions is not apparent in the aircraft measurements, which may be due to on-site management factors that are difficult to capture accurately in national-scale inventories. If not properly accounted for, such seasonal disparities could lead to source misattribution in top-down assessments of methane fluxes.

    View details for DOI 10.1029/2019JG005429

    View details for Web of Science ID 000538019700022

    View details for PubMedID 33614366

    View details for PubMedCentralID PMC7894054