Methane is a potent greenhouse gas and the dominant constituent of natural gas. Measuring and controlling all methane sources, including natural gas, is necessary to limit the adverse consequences of global climate change. This report describes quantitative estimates of methane emissions from some of the California natural gas infrastructure with methane emissions occurring from “well to burner.” To establish a baseline, the research team used a 2013 U.S. Environmental Protection Agency (US EPA) inventory of national natural gas emissions to derive the California bottom-up model. The inventory suggests in-state emissions are about equally split between in-state production and the total of in-state transmission, processing, distribution, and consumption. The team investigated each area using atmospheric measurements and inverse modeling. At the regional level, emissions from production dominate in the Southern San Joaquin and Northern Sacramento Valleys, while distribution- and consumption-related emissions dominate in urban areas like San Francisco Bay Area. Methane emissions from natural gas distribution and consumption in the San Francisco Bay Area California are 1 to 1.6 times the 2013 US EPA bottom-up estimate. Emission measurements from eight natural gas storage fields are consistent with industry reporting to the US EPA, while emissions measured from three refineries were higher than the annual average. Leaks from nine compressed natural gas fueling stations were from 0.03 to 0.1 percent of annual average compressible natural gas retail fuel throughput (the amount of natural gas pumped by the compressors), and there were small but measurable leaks from plugged and abandoned dry-gas wells in the Sacramento River Delta. Finally, leakage measurements for 10 single-family houses were about 0.2 percent of consumption. Benefits include improved knowledge to guide mitigation, identify measurement technologies to verify progress, and reduce the total societal costs of natural gas as an energy resource.
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