Spatial distribution of fossil fuel-derived CO2 using radiocarbon measurement in South Korea influenced by regional characteristics and human activities.

Accelerator mass spectrometry (AMS) is one of the most precise analytical tools for tracing fossil fuel-derived CO2 in the atmosphere. In this study, deciduous tree leaves were collected from Gyeongju and neighboring cities in South Korea to analyze the radiocarbon (Δ14C) characteristics of atmospheric CO2. The measured Δ14C values were used to estimate fossil fuel-derived CO2 concentrations (CO2_ff, ppm) for comparison among the different regions. The sampling locations were expanded incrementally from 2018 to 2024, with 12 sampling sites in 2024. A comparison of Δ14C and CO2_ff revealed clear spatial differences associated with regional characteristics, such as traffic density, population activity, and industrial emissions. Long-term observations from 2018 to 2024 indicated persistent Δ14C depletion in densely populated and industrialized areas, highlighting the sensitivity of radiocarbon to changes in human activity levels. Industrial areas exhibited substantially lower Δ14C values and correspondingly higher (≤23.6 ppm) CO2_ff concentrations than rural areas. These results demonstrate that regional fossil fuel-derived CO2 distributions are influenced by regional differences in human activity.