Two-Year Observation of Fossil Fuel Carbon Dioxide Spatial Distribution in Xi'an City.

The need for atmospheric carbon dioxide (CO2) reduction in the context of global warming is widely acknowledged by the global scientific community. Fossil fuel CO2 (CO2ff) emissions occur mainly in cities, and can be monitored directly with radiocarbon (14C). In this research, annual plants [Setaria viridis (L.) Beauv.] were collected from 26 sites in 2013 and 2014 in the central urban district of Xi'an City. The Δ14C content of the samples were analyzed using a 3 MV Accelerator Mass Spectrometer, and CO2ff concentrations were calculated based on mass balance equations. The results showed that the CO2ff mixing ratio ranged from 15.9 to 25.0 ppm (part per million, equivalent to µmol mol−1), with an average of 20.5 ppm in 2013. The range of measured values became larger in 2014, from 13.9 ppm to 33.1 ppm, with an average of 23.5 ppm. The differences among the average CO2ff concentrations between the central area and outer urban areas were not statistically significant. Although the year-to-year variation of the CO2ff concentration was significant (P < 0.01), there was a distinctly low CO2ff value observed in the northeast corner of the city. CO2ff emissions from vehicle exhaust and residential sources appeared to be more significant than two thermal power plants, according to our observed CO2ff spatial distribution. The variation of pollution source transport recorded in our observations was likely controlled by southwesterly winds. These results could assist in the optimal placement of regional CO2 monitoring stations, and benefit the local government in the implementation of efficient carbon emission reduction measures. [ABSTRACT FROM AUTHOR]