A 12 city survey of urban natural gas leaks

Leaks in the natural gas distribution systems in cities pose a threat to human safety via both explosion hazard and climate change. At one time, the distribution and abundance of these leaks were unknown to science because they fell strictly under the purview of the local distribution companies (LDC's) that manage the distribution pipelines. Lack of transparency about leak activity within and among cities has prevented a public, data-driven conversation about how to manage these leaks in light of cost and safety considerations. Here, we present results of a four-year effort to map natural gas leaks in 12 urban areas across the United States. In a collaboration between Google and Environmental Defense Fund (EDF), high-sensitivity methane analyzers were placed on a set of Google Street View cars and driven through designated regions of each city. Data were analyzed following algorithms that we have published previously, leading to maps of natural gas leak indications (hereafter "leaks") along with estimates of the size of each leak. These maps and the associated data are available on a web site maintained by EDF. Cumulatively, this effort mapped the neighborhoods of over five million Americans and documented the presence of approximately 6,100 natural gas leaks that, together, emit an estimated 5,700 tons of methane per year. Similar to other studies of natural gas leaks, we found that the distribution of leak sizes in this dataset was strongly skewed such that the largest 16% of leaks released 50% of emissions. Among cities, leak density varied roughly 200-fold, ranging from 0.01 to 2 leaks per mile of roadway. The variation in leak density and leak activity among cities was highly correlated with the US federal data (PHMSA) on the abundance of leak-prone pipe for the LDC associated with each city, suggesting that the overwhelming majority of the observed leaks and emissions were due to failures in corrosion-prone pipe. We conclude that these surveys and the data they produce, along with future deployments of similar technology, enable efficient and effective repair and replacement of a system's leakiest infrastructure.