ABSTRACT
Natural gas pipelines are an important source of fugitive methane emissions in lifecycle greenhouse gas assessments but limited monitoring has taken place of UK pipelines to quantify fugitive emissions. This study investigated methane emissions from the UK high-pressure pipeline system (National Transmission System - NTS) for natural gas pipelines. Mobile surveys of CH4 emissions were conducted across four areas in the UK, with routes bisecting high-pressure pipelines (with a maximum operating pressure of 85bar) and separate control routes away from the pipelines. A manual survey of soil gas measurements was also conducted along one of the high-pressure pipelines using a tunable diode laser. For the pipeline routes, there were 26 peaks above 2.1ppmv CH4 at 0.23peaks/km, compared with 12 peaks at 0.11peaks/km on control routes. Three distinct thermogenic emissions were identified on the basis of the isotopic signal from these elevated concentrations with a peak rate of 0.03peaks/km. A further three thermogenic emissions on pipeline routes were associated with pipeline infrastructure. Methane fluxes from control routes were statistically significantly lower than the fluxes measured on pipeline routes, with an overall pipeline flux of 627 (241-1123 interquartile range) tonnes CH4/km/yr. Soil gas CH4 measurements indicated a total flux of 62.6ktCH4/yr, which equates to 2.9% of total annual CH4 emissions in the UK. We recommend further monitoring of the UK natural gas pipeline network, with assessments of transmission and distribution stations, and distribution pipelines necessary.
