2021-09-13

Researchers use sophisticated instruments and machine learning to map California’s methane emission concentration

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These plumes are large enough for researchers from the Jet Propulsion Laboratory (JPL) to ask the facility operator Reported the incident to the local law enforcement agency. This is an important step in the process of better accounting for local gas emissions.

Methane is a short-lived but powerful greenhouse gas. Since the industrial revolution, about 20% of global warming has been caused by methane. Dairy and beef cattle produce methane through their intestines and release it during hiccups. Their manure also produces methane, and when it is stored in a manure tank, it may be a major source of emissions. Oil and natural gas production releases methane from the ground, and the infrastructure that stores and transports methane may leak. When organic materials are broken down by bacteria under anaerobic conditions, landfills are a source of methane.

California’s goal is to reduce this methane emissions, trying to reduce it to 40% below 2013 levels by the end of this decade. But in order to reduce emissions, the state needs to better grasp the source.

The California Air Resources Board (CARB)-the national agency that oversees air pollution control efforts-traditionally estimates greenhouse gas emissions by counting known emission activities. But this method may miss leaks or other fugitive emissions, so CARB staff became interested in measuring emissions in the air to improve the accounting of greenhouse gases and identify mitigation opportunities.

Researchers use sophisticated instruments and machine learning to map California’s methane emission concentration

The picture above shows AVIRIS- Methane measurements taken by the NG instrument while flying over Santa Clarita, California in October 2016 and 2017. The methane emissions from the Sunshine Canyon Landfill are shown in a gradient from yellow to red, with red representing the highest concentration. The graph on the right shows the reduction in methane concentration after implementing improvements to the landfill.

These flights are part of the California Methane Survey, an ongoing project to map the state’s methane emission sources. But before the flight, climate scientists Francesca Hopkins of the University of California, Riverside and Riley Duren of JPL (now at the University of Arizona) began mapping all potential methane sources around the state in order to better focus the limited flight time and prioritize observations.

They decided to use a GIS-based method to absorb many publicly available geospatial data sets to develop a map to help them quickly match the methane plume to possible sources. The research team divided California’s potential methane emission infrastructure into three sectors: energy, agriculture, and waste. This data set is called Methane Emission Sources (Vista-CA) and includes more than 900,000 entries and is available at NASA’s Oak Ridge National Laboratory Distributed Active Archive Center (ORNL DAAC).

From August 2016 to November 2017, a JPL-based team flew a plane equipped with AVIRIS-NG instruments within a range of 22,000 square miles in the state. To speed up data analysis, Duren and colleagues then used machine learning techniques (such as neural networks) to automatically identify smoke plumes detected during flight. At the same time, Talha Rafiq, a graduate student from the University of California, Riverside, developed an algorithm to attribute methane plume observations to the most probable Vista-CA source. These technologies allow the team to share their findings with California facility operators and regulators within a few weeks to alert them to fugitive methane emissions and help expedite remedial measures.

Researchers investigated more than 272,000 individual facilities and equipment components. In these sites, less than 0.2% of infrastructure emissions account for at least one-third of California’s methane stocks. Landfills and composting facilities are responsible for 41% of the emissions measured. Duren, Hopkins and others published their research results in the journal Nature in 2019.

In one case in Sunshine Canyon, the landfill operator confirmed the existence of methane emissions and determined that they were due to problems with surface coverage and gas capture systems. In the following year, operators implemented a series of changes that greatly reduced emissions. A subsequent flyby with AVIRIS-NG confirmed the reduction in methane. These findings were documented by Duren, Daniel Cusworth (a project scientist at the University of Arizona) and others in the 2020 Environmental Research Bulletin.

Data from the survey can be viewed on the methane source search portal. Part of the funding for this research came from NASA’s Collaborative Linkage Program to Advance Earth System Science and the California Prototype Methane Monitoring System in NASA’s Carbon Monitoring System.