Seasonal and Diurnal Variations in XCO<sub>2</sub> Characteristics in China as Observed by OCO‐2/3 Satellites: Effects of Land Cover and Local Meteorology
Hengheng Zhao, Ke Gui, Wenrui Yao, Nanxuan Shang, Xutao Zhang, Xinglu Zhang, Lei Li, Yu Zheng, Zhili Wang, Hong‐Li Ren, Hong Wang, Junying Sun, Jian Li, Huizheng Che, Xiaoye Zhang
Abstract
Abstract Monitoring the dynamics of atmospheric CO 2 is crucial for enhancing comprehension of the carbon cycle. Using column‐averaged dry‐air mole fraction of CO 2 (XCO 2 ) data collected by the Orbiting Carbon Observatory (OCO)‐2 and OCO‐3 satellites during 2020–2021, this study explored seasonal and diurnal variations in XCO 2 characteristics in typical land cover biomes in China, and investigated their relationships with meteorological drivers. Results showed that XCO 2 products retrieved by OCO‐2 and OCO‐3 have good agreement with Total Carbon Column Observing Network measurements, with average deviations of 0.8 and 1.2 ppm, respectively. The satellite observations revealed XCO 2 hotpots located mainly in central and eastern China, and areas of low XCO 2 values in western China, with a seasonal curve that was highest (lowest) in spring (summer). The largest seasonal cycle amplitude (∼9 ppm) of XCO 2 was observed in forest areas, highlighting its key role in carbon exchange. Additionally, XCO 2 was found to have a near‐sinusoidal diurnal pattern, characterized by rapid decrease in the early morning as photosynthesis resumed after sunrise, as indicated by the sun‐induced chlorophyll fluorescence (SIF), a peak at around midday, and subsequent decrease as SIF increased after mid‐afternoon. Urban regions had the highest diurnal cycle amplitude (∼6 ppm) among biomes. Statistical analyses revealed seasonal shift and nonlinear variation in the relationships between XCO 2 and meteorological variables, suggesting that CO 2 uptake is influenced by favorable humidity conditions. These relationships also provide insight into the sensitivity and adaptability of XCO 2 to meteorological factors in diverse ecosystems such as savanna and grassland.