The Boston metro and New York City metro areas were impacted by COVID-19 earliest and hardest in the United States, with incidence and mortality rates among the highest on the globe at the time. Shutdowns in these cities were among the most complete in the United States. Behavioral changes were significant and continue to this day. Many companies and schools have extended work/learn from home guidelines to 2021 and beyond. These profound changes in how people work, move, and recreate, have changed the urban atmospheric composition dramatically. During the spring shutdown, the project team observed declines in methane mixing ratios of ~40% in Boston and New York, relative to previous months and years. Do the large declines observed in methane indicate ?lost and unaccounted for? methane or an incorrectly attributed source? Are end-user methane emissions being erroneously attributed to leaking pipe infrastructure? This project focuses on the COVID-19 shutdown as a unique opportunity to observe changes in the major sources of methane in dense urban areas, in order to help determine which sector contributes emissions that fill the large gap between bottom-up and top-down analyses of urban emissions. This project will (a) calculate methane emissions sampled by urban core sites for the full year, (b) develop baseline and COVID-19 shutdown period high resolution methane inventories, and (c) test a suite of hypotheses about causal mechanisms for emissions change. Using these insights, the project team will refine bottom-up emissions models and reassess the relative contributions of pipeline, compressor station, and beyond-the-meter sources.