Evaluation of the Potential Use of Satellite-Derived XCO2 in Detecting CO2 Enhancement in Megacities with Limited Ground Observations: A Case Study in Seoul Using Orbiting Carbon Observatory-2. Asia-Pacific

Exact assessment of urban atmospheric CO₂ enhancement, which is higher than background CO₂ concentrations, is critical to mitigate carbon emissions in the city. However, ground-based atmospheric CO₂ measurements covering the diverse landscape across the city are still limited. This study utilizes the column integrated CO₂ concentration (XCO₂) data obtained from the NASA Orbiting Carbon Observatory-2 (OCO-2) to evaluate urban CO₂ enhancements over Seoul Capital Area (SCA) of South Korea for the period 2014–2018. In this study, Jirisan National Park (JNP), which is the cleanest area on the same orbit track with SCA, is defined as the background area considering its strong vegetation activity and low anthropogenic carbon emissions. By comparing XCO₂ between SCA and JNP based on wind speed, we find an apparent increase in XCO₂ by 1.71 to 2.21 ppm over SCA only on the days with wind speed less than 4 m s⁻¹. Strong wind speed (e.g., over 4 m s⁻¹) disrupts the identification of XCO₂ enhancements over SCA due to atmospheric mixing between SCA and JNP. In addition, we compare estimated XCO₂ differences between SCA and JNP from OCO-2 with other low-resolution data. This increase in XCO₂ over SCA is only observed in OCO-2. Overall, our results suggest that high-resolution satellite remote sensing of XCO₂ constrained by wind speed has strong potential to open up the possibility of identifying atmospheric CO₂ enhancements in the city where ground-based observations are limited.