The California Methane Survey

Methane point source emissions play an important role in the human (anthropogenic) methane inventory and present unique opportunities for mitigation. The researchers conducted a comprehensive survey of facilities and components in California, spanning the oil and gas, manure management, and waste management sectors, using an airborne imaging spectrometer capable of rapidly mapping methane plumes. Five campaigns were conducted over several months from 2016 to 2018, resulting in the detection, geolocation, and quantification of 564 strong methane point sources. This represents a major advance in the use of remote sensing to rapidly and repeatedly assess large areas at high spatial resolution for a poorly characterized population of methane point sources. The team estimated that emissions from methane point sources in California contribute more than a third (34 to 46 percent) of the state’s methane inventory for 2016. Methane super-emitter activity occurs in every surveyed sector. Over the entire population of observed point sources, 10 percent of sources contributed nearly 60 percent of emissions. The largest methane point source emitters in California are 32 landfills and composting facilities exhibiting persistent, potentially anomalous activity. Production is responsible for nearly 80 percent of point source emissions associated with California’s oil and gas sector. Point source emissions from natural gas infrastructure are primarily associated with a relatively small number of processing plants, compressor stations, refineries, and gas fired power plants. The project identified five low pressure natural gas leaks that were subsequently repaired by operators. This work highlights the potential for efficient point source monitoring to enable mitigation of a broad class of methane super-emitters, representing a significant contribution to California’s climate stabilization targets, reduced natural gas product loss, and early warning of potentially hazardous leaks.