Variations in CO2 Fluxes at the Surface-Atmosphere Interface Within the Seoul Metropolitan Area

The monitoring and comprehension of CO2 fluxes in urban environments face challenges due to severe spatiotemporal heterogeneity of emissions sources and limited measurement networks. This issue is particularly critical for large cities, which stand as major contributors to anthropogenic CO2 in the climate system. Focusing on Seoul, Korea, this study analyzes CO2 fluxes at eight surface energy balance sites spanning 2017–2018. These sites comprise six urban locations (vegetation-area fraction < 15%) and two suburban sites (vegetation-area fraction > 60%), aiming to attribute the fluxes to local land-use and business types. To compare with rural area, CO2 fluxes from the Boseong Standard Meteorological Observatory, characterized by rice paddy, were utilized. Results reveal that CO2 flux variations at suburban sites are predominantly influenced by vegetation, while disparities between urban and suburban sites arise from differences in vegetation-area fraction and anthropogenic CO2 emissions.  For the CO2 fluxes at the urban sites; (1) vehicle traffic (traffic) and heating-fuel consumption (heating) contribute > 80% to the total, (2) vegetation effects are minimal, (3) the seasonal cycle is driven mainly by heating, (4) the contribution of heating is positively related to the building-area fraction, (5) the annual total is positively (negatively) correlated with the commercial-area (residential-area) fraction, and (6) the traffic at the commercial sites depend further on the main business types to induce distinct CO2 flux weekly cycles. This research demonstrates that comprehending and estimating CO2 fluxes in sizable urban areas necessitate meticulous site selections and analyses founded on detailed consideration of the refined land-use and business types, going beyond the commonly used single representative land-use type in contemporary studies.