Spatial Variations Of Atmospheric CO₂ And CH₄ Concentrations And Their Carbon Isotopes In China

The combustion and release of urban fossil fuels and land use to different degrees are seriously affecting the space-time changes of atmospheric carbon cycle and stable carbon isotopes.This study takes CO₂,CH₄ and carbon isotopes of the near surface atmosphere in winter in many administrative regions of China as the research object.The instantaneous value of the spatial variation of greenhouse gases in large-scale region is given by real-time dynamic measurement.For further study,combined with real-time measured data and reanalysis data,the influences of meteorological factors and human activities are qualitative analyzed.The results have critical significance for enhancing the understand of urban carbon cycle,reveal the impact of urbanization and the spatial difference of greenhouse gas emissions,which will provide an crucial basis for further research on urban carbon cycle.The main results and conclusions are as follows.The spatial variation characteristics of near-surface atmospheric CO₂,CH₄ and their carbon isotope ratios are revealed.The results show that the concentrations of near-surface atmospheric CO₂ is lower in the north and southwest of China,and higher in the central and eastern regions.In general,there is no obvious spatial distribution characteristics of?¹³C-CO₂ near the surface,and the carbon isotope depletion areas are distributed in in Beijing-Tianjin-Hebei region,Hunan,Hubei and Sichuan.The spatial heterogeneity of near-surface atmospheric CH₄ is obvious,the concentration of CH₄ is higher in the Beijing Tianjin Hebei region,the junction of Inner Mongolia and Ningxia,Henan-Hebei border and Sichuan.The secondary high value appeared in the middle east of Yunnan,the central south of Sichuan and the southeast of Heilongjiang Province.The spatial distribution of?¹³C-CH₄ in the near-surface atmosphere is characterized by carbon isotope dilution in the northeast China and enrichment in the central and western China.The near-surface atmospheric CO₂ and CH₄ concentrations in most cities show significant urban dome effects on urban-suburban spatial gradients.The concentrations of CO₂ and CH₄ in the urban near-surface atmosphere are significantly higher than those in the suburbs,and this effect shows different degrees in different cities.The?¹³C of near-surface atmospheric CO₂ and CH₄ showed a stronger fluctuation trend in urban areas than in suburbs.In urban-suburban spatial gradient,low wind is not the main factor affecting near-surface gas concentration.More intensive transportation and production activities in urban areas dominate the spatial differences between urban and suburban areas.At the regional scale,human activities have a major impact on atmospheric CO₂ and CH₄.According to the variation of?¹³C,the potential sources of urban CO₂ and CH₄emissions were qualitatively analyzed.In the winter heating season,the increase of near-surface CO₂ concentration in urban areas is due to fossil fuel combustion and automobile exhaust emissions,which is similar in northern and southern regions.The reasons for the increase of atmospheric CH₄ concentration near the ground are different.In southern cities,it is mainly caused by escape in the process of distribution end use,while in northern cities,it is mainly caused by fossil fuel combustion.