Severe spatiotemporal heterogeneity of emissions sources and limited measurement networks have been hampering the monitoring and understanding of CO 2 fluxes in large cities, a great concern in climate research as big cities are among the major sources of anthropogenic CO 2 in the climate system. To understand the CO 2 fluxes in Seoul, Korea, CO 2 fluxes at eight surface energy balance sites, six urban (vegetation-area fractio...