Methane emissions from natural gas production and use: reconciling bottom-up and top-down measurements

Methane emissions from the natural gas supply chain are a key factor in determining the greenhouse gas footprint of natural gas production and use. Recent estimates of these emissions have varied widely, because of the large population of sources, because of different measurement and estimation approaches, and because of extreme values of emission rates from individual sources that are much larger than population average values of emission rates from sources in the same category (a 'fat-tail' distribution). Reconciling differences between ambient methane concentration measurements (top-down methods) and direct measurement of emissions from individual sources (bottom-up methods) is critical to understanding methane emissions from the natural gas supply chain. A combination of top-down and bottom-up approaches is recommended.