National Center for Sustainable Transportation

Natural gas provides an alternative to petroleum-based fuels as an energy source that is being more widely adopted across multiple sectors in California. The viability of natural gas depends on its total life cycle emissions, specifically of those of methane. This paper addresses the possibility of and reason for fugitive emissions of methane from the transportation sector by surveying and quantifying methane plumes from compressed natural gas (CNG) and liquified natural gas (LNG) storage tanks at vehicle fueling facilities in the greater Los Angeles metropolitan area. This project used methane plume images provided by airborne imaging spectroscopy, collected by NASA’s AVIRIS-NG mission, to identify large methane point sources originating from CNG and LNG infrastructure. The periodic methane plume observations were converted into emission rates to provide an estimate for potential methane emissions from NG storage facilities across California. For the population of facilities that were analyzed, four had natural gas storage tanks with emission rates that are higher than the maximum rate specified by the tank manufacturers. The significant disparity between the expected emission rate and the actual emission rate can be explained by tank malfunction, as the number of observed plume events are far higher than what would be expected for a fully operational tank. If the tank malfunction rates found in the group that was analyzed were applied to the entire population of California CNG and LNG facilities, total emissions may be up to 1300 kg CH4 per hour, suggesting a need for leak monitoring and repair to prevent excessive methane emissions from this sector. 

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