Finding the Missing Link in Methane Emission Inventories Using Aircraft and Mobile Observations

Methane emissions are associated with a wide range of human activities and contribute to climate radiative forcing as an effective absorber of terrestrial longwave radiation. In this study, we detected high levels of methane outside metropolitan areas via aircraft and mobile measurements that were conducted in February and March 2021. The emission sources were investigated using a particle dispersion model that combines the Weather Research and Forecasting model and the Stochastic Time-Inverted Lagrangian Transport model. Overall, the average measured methane emissions were 239.4–313.5 ppb (12.6 – 16.5 %) higher than the monthly average methane levels observed at the Mauna Loa Observatory in Hawaii. In addition, methane concentration hotspots were found to be 190.2–380.8 ppb (10 – 20 %) higher than the concentrations of the surrounding areas. According to the footprint analysis of four local methane hotspots, high methane concentrations appear to be associated with intensive pig farm areas, industrial complexes, industrial wastes dumps, and landfills. However, as there were significant methane emission sources that were hidden and thus excluded from the methane inventory, the current estimates of methane emissions may be underestimated. This study shows that more attention is needed to monitor methane leaks from both unknown and known methane emission sources. We also urge the preparation of a more reliable methane budget to achieve carbon neutrality through regular high-resolution monitoring systems.