Atmospheric Fossil Fuel CO_2 Traced by Δ~(14)C in Beijing and Xiamen, China: Temporal Variations, Inland/Coastal Differences and Influencing Factors

摘要

One year of atmospheric Δ~(14)CO_2 were observed in 2014 in the inland city of Beijing and coastal city of Xiamen, China, to trace temporal CO_(2ff) variations and to determine the factors influencing them. The average CO_(2ff) concentrations at the sampling sites in Beijing and Xiamen were 39.7 ± 36.1 ppm and 13.6 ± 12.3 ppm, respectively. These contributed 75.2 ± 14.6% and S9.1 ± 26.8% to their respective annual ΔCO_2 offsets over background CO_2 concentrations. Significantly (p ＜ 0.05) high CO_(2ff) values were observed in winter in Beijing. We did not find any significant differences in CO_(2ff) values between weekdays and weekends. Diurnal CO_(2ff) variations were plainly evident, with high values between midnight and 4:00, and during morning and afternoon rush hours. The sampling site in the inland city of Beijing displayed much higher CO_(2ff) inputs and overall temporal variations than the site in the coastal city of Xiamen. The variations of CO_(2ff) at both sites were controlled by a combination of emission sources, topography, and atmospheric dispersion. In particular, diurnal observations at the urban site in Beijing showed that CO_(2ff) was easily accumulated under the southeast wind conditions.