Natural gas dominates CH4 emissions in a Tokyo residential area based on eddy covariance measurements of CH4 and C2H6

Urban methane (CH 4 ) emissions are an important but poorly constrained component of the urban greenhouse gas budget, particularly in terms of source attribution. We conducted quasi-continuous eddy covariance measurements of CH 4 and ethane (C 2 H 6 ) fluxes in a densely populated residential area of metropolitan Tokyo from May 2024 to December 2025 to characterize temporal variability, spatial heterogeneity, and source contributions. The strong correlation between CH 4 and C 2 H 6 fluxes enabled tracer-based attribution of total CH 4 emissions to natural gas-related and biogenic sources. CH 4 emissions exhibited distinct diurnal, weekly, and seasonal patterns. Natural gas-related emissions accounted for more than 80% of the annual total, whereas biogenic emissions were minor. Wind-direction analyses revealed spatial heterogeneity associated with land use within the flux footprint. Annual CH 4 emissions were estimated at 35.2–35.7 g CH 4 m -2 yr -1 . Mobile measurements corroborated the prevalence of natural gas-related sources in residential and commercial areas. These natural gas-related emissions are not explicitly represented in the local government emission inventory. These findings show that natural gas use is a dominant and spatially variable component of CH 4 emissions in urban residential environments in Japan, underscoring the need for improved observational constraints on urban greenhouse gas inventories and mitigation strategies.