As California chokes, landfills account for 41 per cent of methane emissions in state
The landfills of California are the top emitters of methane, a powerful greenhouse gas that is second only to carbon dioxide as a climate-warming agent resulting from human activity.
A relatively small number of high emitting point sources - about 700 pieces of infrastructure - are responsible for at least a third of total methane emissions in California, according to a team of researchers who mapped the exact locations responsible for methane emissions.
Waste management is the largest methane point source emission sector in California - 41% in all - driven by a small fraction of landfills. The team - which includes researchers from Jet Propulsion Laboratory, California Institute of Technology, Pasadena, US; University of Arizona, US; and University of California Riverside, US, among others - only observed these plumes at 30 out of 270 surveyed facilities.
The researchers examined 272,000 facilities and components using an airborne imaging spectrometer that can rapidly map methane plumes. Their analysis shows that less than 0.2% of the infrastructure examined is responsible for 34-46% of total methane emissions in California.
The team further says that just 10% of the sources, dubbed as super-emitters, are responsible for about 60% of the emissions.
Methane emissions from manure management at large dairies and the oil and gas sector each contributed about 26% of emissions, shows analysis. The scientists caution that if similar patterns occur in other key regions globally, they estimate that methane super-emitters could account for up to 10% of the “climate forcing from greenhouse gas emissions.”
“We conducted five campaigns over several months from 2016 to 2018, spanning the oil and gas, manure-management and waste-management sectors, resulting in the detection, geolocation, and quantification of emissions from strong methane point sources. We estimate net methane point-source emissions in California to be 0.618 teragrams per year, equivalent to 34-46% of the state’s methane inventory for 2016. Methane ‘super-emitter’ activity occurs in every sector surveyed, with 10% of point sources contributing roughly 60% of point-source emissions,” says the study published in Nature.
It says: “The largest methane emitters in California are a subset of landfills, which exhibit persistent anomalous activity. Methane point-source emissions in California are dominated by landfills (41%), followed by dairies (26%) and the oil and gas sector (26%). Our data have enabled the identification of 0.2% of California’s infrastructure that is responsible for these emissions.”
The researchers looked at point sources - typically less than 10 meters across - that emit plumes of highly concentrated methane. Data on point-source emissions have been sparse and typically lack sufficient spatial and temporal resolution to guide their mitigation and to assess their magnitude accurately.
Some examples of point sources include individual pieces of natural gas infrastructure, oil wells, refineries, gas-capture systems in landfills, wastewater treatment plants, manure management systems at large dairies, and wildfires.
The study also found that nearly 70% of the observed oil and gas point source emissions were associated with oil production in the southern San Joaquin Valley.
“Our methane emission estimates for petroleum refineries in California are 4.5 times higher than those reported to the EPA (Environmental Protection Agency),” says the team.
According to the researchers, many of these methane super-emitters appear to be highly intermittent and due to random malfunctions or leaks spanning the energy, waste, and agriculture sectors.
“In several test cases, we shared our data with facility operators who used it to guide confirmation and repair efforts. Frequent high-resolution remote-sensing of priority regions can help improve methane budgets and accelerate mitigation action, particularly when combined with complementary measurement systems,” says the team.
Several factors prompted scientists to focus on methane. “Methane is a powerful greenhouse gas, second only to carbon dioxide as a climate-forcing agent resulting from human (anthropogenic) activity. The growth rate of methane in the atmosphere is due to a complex combination of natural and anthropogenic emissions and natural removal processes. The exact causes for observed changes in the methane growth rate over time remain uncertain due to incomplete data and disagreements between different measurement methods. Methane emissions and their causes at local and regional scales remain particularly uncertain,” say experts.
Methane is targeted for emissions mitigation by California and other jurisdictions worldwide, according to scientists.
“Methane vented to the atmosphere from leaks in natural gas infrastructure – if not promptly detected and repaired - can result in costly product loss and (in sufficiently large quantities) a combustion hazard,” says the team.