Research

Current Research

1. Global Hydrogen Budget

There is increasing interest in hydrogen (H2) as a climate change solution that could help decarbonize industry, transport, and electricity generation. When produced by electrolysis with renewable energy, hydrogen, in principle, can be produced and consumed with zero carbon emissions. Yet, increasing the production, transport, and use of H2 will lead to increased human emissions of H2 to the atmosphere due to accidental or intentional leaks, which will affect the global H2 budget, greenhouse gas concentrations in the atmosphere, and the climate.

H2 concentrations in the atmosphere have been increasing since pre-industrial. The reason for this rise is not well understood due to an incomplete understanding of H2 sinks and sources. H2 in the atmosphere reacts with and consumes hydroxyl (OH) radicals, which are an important sink of short-lived greenhouse gasses such as CH4.  Thus, an increase in atmospheric H2 reduces OH concentrations in the atmosphere and causes “indirect” warming by prolonging the atmospheric lifetime of other greenhouse gasses. Studies estimate a global warming potential (GWP) for H2 of 11 ± 5 over a hundred-year time horizon, which is 6 to 16 times stronger than CO2 and about one-third of CH4.

To assess the climatic consequences of current changes in atmospheric H2, and to explore the potential climate impacts of hydrogen leakage in a future hydrogen economy, this project aims to examine the trends of H2 sources and sinks over the past three decades (1990-2019) and construct a new global H2 budget for the most recent decade. This project is supported by the Global Carbon Project as a new initiative.

Related publications:

1). Zutao Ouyang*, Rob Jackson, Josep Canadell, Yuanhong Zhao, Catherine Morfopoulos, et al., Global Hydrogen Budget. (in prep and available upon request)

2. Global Wetland CH4 Synthesis

Wetlands, both natural wetlands and man-made wetlands (i.e., paddy rice), are important CH4 emitters and meanwhile major sources of uncertainty in the current understanding of the global CH4 budget. The goal of this project is to understand and predict CH4 fluxes across wetlands globally. My colleague and I first took advantage of the continuous and ecosystem-scale measurement of Eddy Covariance to understand the controls and timing of CH4 flux dynamics across global natural wetlands and paddy-rice. Then, based on synthesized CH4 flux data, and our understanding of important drivers, we developed machine-learning approaches to spatially upscale wetland emissions globally to further understand global total emissions and the spatiotemporal variation of CH4 flux.

We have so far standardized, post-processed (i.e., partitioned and gap-filled), and released as FLUXNET-CH4 including 81 sites, most of which are wetlands. We also synthesized 23 paddy-rice sites that measured CH4 using Eddy Covariance.

The main objective of my participation is to use machine learning to spatially upscale CH4 emissions across global natural wetlands and paddy rice using geospatial big data. Our first product of paddy rice CH4 emissions across Monsoon Asia is available here: https://doi.org/10.5281/zenodo.7145497.

Paddy rice methane emissions across Monsoon Asia

Related publications:

1). Zutao Ouyang*, Robert B.Jackson, Gavin McNicol,Etienne Fluet‑Chouinard,Benjamin R.K. Runkle,Dario Papale, Sara Knox, et al. 2022. Paddy‑rice Methane Emission across Monsoon Asia. Remote Sensing of Environment. https://doi.org/10.1016/j.rse.2022.113335

2). Gavin McNicol G, Etienne Fluet‑Chouinard, Zutao Ouyang, et al. Upscaling Wetland Methane Emissions From the FLUXNET-CH4 Eddy Covariance Network (UpCH4 v1.0): Model Development, Network Assessment, and Budget Comparison. 2023, AGU Advances, https://doi.org/10.1029/2023AV000956

3). Kyle B Delwiche, Sarah Helen Knox, Avni Malhotra, Etienne Fluet‑Chouinard, Gavin McNicol, Sarah Feron, Zutao Ouyang, et al. FLUXNET‑CH4: A global, multi‑ecosystem dataset and analysis of methane seasonality from freshwater wetlands. Earth System Science Data. https://doi.org/10.5194/essd-2020-307

4). Jeremy Irvin, Sharon Zhou, Gavin McNicol, Fred Lu, Vincent Liu, Etienne Fluet‑Chouinard, Zutao Ouyang, et
al. 2021. Gap‑filling eddy covariance methane fluxes: Comparison of machine learning model predictions
and uncertainties at FLUXNET‑CH4 wetlands. Agricultural and Forest Meteorology. https: //doi.org/10.1016/j.agrformet.2021.108528

5). Sara Helen Knox, et al. 2021. Identifying dominant environmental predictors of freshwater wetland methane fluxes across diurnal to seasonal time scales. Global Change Biology. 1‑111. https://doi.org/10.1111/gcb.15661

3. Urban Emission, Climate Change, and Energy Consumption

Emission: CH4, the primary component of natural gas, is a potent greenhouse gas used in over half of all residential homes in the United States. Although there is much ongoing research regarding methane emissions from various sources from production through distribution of natural gas, post-meter emissions at homes are understudied and often overlooked. To this day, the United States Environmental Protection Agency offers no estimate for residential home leakage in their greenhouse gas emission inventory.

In this project, we measure emissions of methane and air pollutants from residential natural gas appliances, such as cooktops, ovens, water heaters, and furnaces, and then use statistics, machine learning, and geospatial techniques to upscale total emissions from California and the United States.

Gas stoves, in particular, release combustion products directly into indoor air. Some of these compounds can pose a health concern if concentrations reach unhealthy levels. Therefore, we also measure health pollutants such as NO2, NO, CO, and BTEX from gas stoves.

Check Stanford Home for more details.

Methane and NOx Emissions from Natural Gas Stoves in Residential Homes (Lebel et al., 2022)

Related publications:

1). Eric D. Lebel, Colin J. Finnegan, Zutao Ouyang, Robert B. Jackson. 2022. Methane and NOx Emissions from Natural Gas Stoves, Cooktops, and Ovens in Residential Homes. Environmental Science & Technology, https://doi.org/10.1021/acs.est.1c04707

2). Yannai S. Kashtan, Robert B. Jackson, Metta Nicholson, Colin Finnegan, Zutao Ouyang, Eric D. Lebel, Seth B.C. Shonkoff, Drew R. Michanowicz. Gas and 2023. Propane Combustion from Stoves Emits Benzene and Increases Indoor Air Pollution. Environmental Science & Technology, https://doi.org/10.1021/acs.est.2c09289

Climate Change and Energy Consumption: Urbanization not only contributes to climate change by increasing anthropogenic GHG emissions and by changing carbon, water, and energy cycling but also respond to climate change in terms of energy consumption pattern, technology, and social-economical processes. In this project, we study the bi-directional interactions between urbanization and climate change.

Change of Albedo Caused by Projected Urbanization from 2018 to 2050 under SSP2-4.5

Related publications:

  1. Zutao Ouyang, Pietro Sciusco, Tong Jiao, Sarah Feron, Cheyenne Lei, Fei Li, Ranjeet John, Peilei Fan, Xia Li, Christopher A Williams, Guangzhao Chen, Chenghao Wang, Jiquan Chen. 2023. Albedo changes caused by future urbanization contribute to global warming. Nature Communications. https://www.nature.com/articles/s41467-022-31558-z
  2. Chenghao Wang, Jiyun Song, Dachuan Shi, Janet L. Reyna, Henry Horsey, Sarah Feron, Yuyu Zhou, Zutao Ouyang, Ying Li & Robert B. Jackson. 2023. Impacts of climate change, population growth, and power sector decarbonization on urban building energy use. Nature Communications. https://www.nature.com/articles/s41467-023-41458-5