A Seven Year Top-Down Analysis of Methane Emissions from Natural Gas Infrastructure in the Boston Urban Region

With the withdrawal of the US from the Paris Climate Accord, cities and states are leading US actions towards reducing greenhouse gas emissions. Since 2014, Massachusetts has implemented new laws aimed at identifying and repairing natural gas leaks to reduce methane emissions. To assess the efficacy of these policies, traceable methods for tracking changes in emissions are essential. We use continuous measurements of atmospheric methane from five sites in and around Boston in an inverse analysis to quantify methane emissions from 2012-2019. We combine these measurements with ethane measurements, a high-resolution CH₄ emission inventory and a Lagrangian particle dispersion model to determine the regional loss rate from natural gas infrastructure and its changes over seven years. We assess the model framework uncertainties using a bootstrap analysis and determine the minimum detectable trend. This assessment will provide stakeholders with critical information to assess mitigation efforts in Boston and surrounding areas.