Seasonal and Diurnal Variations in XCO 2 Characteristics in China as Observed by OCO‐2/3 Satellites: Effects of Land Cover and Local Meteorology

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. Measuring CO 2 concentrations helps us gain better understanding of the carbon cycle in the context of climate change. China is among the world's main emitters of carbon and it has pledged to achieve carbon neutrality. To create effective strategies for the mitigation of atmospheric CO 2 , it is important to investigate the CO 2 dynamics on multiple time scales. Using observations from the OCO‐2 and OCO‐3 carbon‐monitoring satellites, we characterized the seasonal and diurnal variations in column‐averaged abundance of CO 2 (XCO 2 ) across biomes and examined the impact of meteorological factors. Our findings revealed a near‐sinusoidal pattern in the hourly variation of XCO 2 over biomes, and suggested XCO 2 seasonal variability varie