Beyond CO2: why methane slip measurement matters for gas producing facilities

In Australia, gas producing facilities must report greenhouse gas emissions under the National Greenhouse and Energy Reporting (NGER) Act 2007 and comply with the Safeguard Mechanism if their total emissions exceed 100,000 tonnes CO2-equivalent (CO2-e) per year. Emissions are measured in CO2-e, which accounts for all covered gases weighted by their global warming potential (GWP). Methane (CH4) is explicitly listed as a covered gas. Methane has a GWP of 28, meaning 1 tonne of methane has the same climate impact as 28 tonnes of carbon dioxide. This weighting makes methane slip (unburned methane released from combustion in gas-fired engines) critical to quantify. We have measured methane concentrations of up to 2849 ppm, contributing approximately 55% of total CO2-e emissions for the same engine. If methane slip is not measured or accounted for, facilities may significantly underreport their actual CO2-e emissions, potentially by a large margin. Accurate measurement of methane engine emissions with fourier transform infrared spectroscopy can be reliably used to measure methane slip from combustion sources. It also allows sites to tune the engines to work at reducing methane slip in real time, making it a valuable tool for ensuring compliance. Facilities exceeding NGER thresholds and falling under the Safeguard Mechanism are assigned baseline emission targets and must surrender Australian carbon credit units or safeguard mechanism credits to offset excess emissions. The baseline declines annually by about 4.9%. Given methane’s high GWP, even small unmeasured methane slip can have disproportionate impacts on both compliance obligations and environmental performance.