Spatial variations in daytime methane and carbon dioxide emissions in two urban landscapes, Sakai, Japan
Tsugumi Takano, Masahito Ueyama
Abstract
To obtain an accurate understanding of carbon dioxide (CO 2 ) and methane (CH 4 ) emissions from urban areas, it is important to estimate their spatial variations because the heterogeneous nature of urban land use results in different emissions patterns. We measured CH 4 and CO 2 fluxes from two urban landscapes in Japan with the eddy covariance method and evaluated the spatial distributions of fluxes by combining flux footprint analysis and mobile measurements of gas concentrations. CH 4 hotspots were identified at sewage plants, oil refineries , and natural gas facilities in the urban center. The fluxes (60 ± 65 nmol m −2 s −1 ) affected by hotspots were higher than those in the suburban and residential areas (22 ± 30 nmol m −2 s −1 ). High CH 4 concentrations of up to 5130 ppb from the hotspots were also observed in the mobile measurements. The measured fluxes showed that the study area generally acted as a CH 4 source irrespective of the presence of hotspots. The mobile measurements suggested several CH 4 sources: gas leaks from natural gas networks, sewage pipes, gas-powered air conditioners, and moats. The CO 2 fluxes were larger in commercial and industrial areas than residential and suburb areas, and fluxes from vegetated areas were nearly CO 2 -neutral in the daytime.