CO2 in Beijing and Xianghe Observed by Ground-Based FTIR Column Measurements and Validation to OCO-2/3 Satellite Observations

Monitoring the atmospheric CO2 columns inside and around a city is of great importance to understand the temporal-spatial variation of XCO2 near strong anthropogenic emissions. In this study, we use two FTIR CO2 column measurements in Beijing (Bruker EM27/SUN) and Xianghe (Bruker IFS 125HR) between 2019 and 2021 to investigate the differences of XCO2 between Beijing (urban) and Xianghe (suburb) in North China and to validate the OCO-2 and OCO-3 satellite XCO2 retrievals. The mean and standard deviation (std) of the Delta XCO2 between Beijing and Xianghe (BeijingXianghe) observed by two FTIR instruments are 0.206 +/- 1.736 ppm, which has a seasonal variation and varies with meteorological conditions (wind speed and wind direction). The mean and std of the XCO2 differences between co-located satellite and FTIR measurements are -0.216 +/- 1.578 ppm in Beijing and -0.343 +/- 1.438 ppm in Xianghe for OCO-2 and 0.637 +/- 1.594 ppm in Beijing and 1.206 +/- 1.420 ppm in Xianghe for 000-3. It is found that the 000-3 snapshot area mode (SAM) measurements can capture the spatial gradient of XCO2 between urban and suburbs well. However, the FTIR measurements indicate that the 000-3 SAM measurements are about 0.9-1.4 ppm overestimated in Beijing and Xianghe.