[¹³ C-based Sources Partitioning of Atmospheric CO₂ During Youth Olympic Games, Nanjing]

Observations of urban atmospheric CO₂ molar fraction and its ¹³ C isotope composition (δ¹³ C) is of great importance to interpret the effect of anthropogenic and biologic sources on local or regional carbon cycle. High-frequency in-situ observation on atmospheric in urban airsheds was performed during Youth Olympic Games (YOG) in Nanjing. The hourly, diurnal and daily differences of CO₂ concentration and its δ¹³ C between the period with and without temporary CO₂ emission controls were compared. The results showed that short-term emission reduction measures could cause 21×10^-6 decrease in atmospheric CO₂ concentration in a regional and short-term scale. The reduction of coal combustion during YOG in YRD was about 5%. The overall isotopic signature of local surface sources δ¹³ C_S in Yangtze River Delta (YRD) was determined by Miller-Tans, and the isotopic signatures of anthropogenic and natural sources in YRD were also determined based on literature investigation. According to the above results, the surface net CO₂ flux, plant flux and anthropogenic flux in YRD were quantified using mass-balance equation. The CO₂ emission from cement production (non-energy industrial process) was the key human factor of high atmospheric δ¹³ C of CO₂ in YRD during summer (2.36‰). The plant effect could offset 23% to 39% anthropogenic CO₂ emission in YRD during summer. In this study, we tried to provide new solution to partition carbon sources in urban areas by combining top-down atmospheric observation and traditional IPCC's emission inventory.