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 CS 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.
Keywords: Yangtze River Delta; Youth Olympic Game; high-frequency in-situ observation; stable isotope δ13 C; urban atmospheric carbon dioxide.