Analysis on the variations of atmospheric CO_2 concentrations along the urban-rural gradients of Chinese cities based on the OCO-2 XCO_2 data

摘要

Anthropogenic CO2 emissions contribute the most to the growth of atmospheric CO2 concentrations. These emissions are largely concentrated in urban areas where human activities are intense. Studies have been conducted to explore the urban and rural difference in CO2 concentrations based on ground-based measurements. The launch of NASA's Orbiting Carbon Observatory-2 (OCO-2) satellite provides a new opportunity to monitor CO2 concentrations and their spatial and temporal variations at city scale. The objective of this study is to analyse the spatial and temporal distributions of CO2 concentrations along the urban-rural gradients of Chinese cities, using the column averaged CO2 dry air mole fraction (XCO2) data derived from OCO-2. We used both conceptual and physical urban-rural gradients to analyse variations in CO2 concentrations over space. The results show that the urban and rural difference in CO2 concentrations of these cities can be monitored. And, the seasonal variations of CO2 concentrations in these cities can also be detected using the XCO2 data. Moreover, the variations in CO2 concentrations along the urban-rural gradients have four main types with significant enhancements of CO2 concentrations were observed in urban areas, urban-rural transitional areas, rural areas, and without regular patterns, respectively. The results are generally different from the common assumption that CO2 concentrations peak in central urban areas and decline in rural areas. In conclusion, the XCO2 data can be used to analyse the spatial-temporal variations of CO2 concentrations along the urban-rural gradients of Chinese cities, and the results have important policy implications for mitigating CO2 emissions.