Tracing fossil fuel CO2 using D14C in Xi'an City, China

Radiocarbon can be used to trace fossil fuel CO2 (CO2ff) in the atmosphere, because radiocarbon has been depleted in fossil fuels. Here we present our study on the spatial distribution and temporal variations of CO2ff in Xi&#39;an City, China using D14C of both green foxtail (Setaria viridis, L. Beauv.) leaf samples and urban air samples collected in the recent years. Our results show that the CO2ff indicated by green foxtail ranged from 14.7 &plusmn; 1.7 to 52.6 &plusmn; 1.7 ppm, reflecting high CO2ff mole fractions in downtown, industrial areas, and at road sites, and low CO2ff mole fractions in public parks. Meanwhile, the monthly CO2ff reflected by air samples showed higher value in winter (57.8 &plusmn; 17.1 ppm) than that in summer (20.2 &plusmn; 9.8 ppm) due to the enhancement usage of coal burning and the poor dispersion condition of atmosphere. This study displays that the increased fossil fuel emission is associated with the fast development of Xi&#39;an City in China. It is worth mentioning that the green foxtail samples can be used to map out the CO2ff spatial distribution on large scale quickly and conveniently, while the air samples can be used to trace the CO2ff temporal variations with high resolution effectively. Therefore the D14C of both green foxtail and air samples is a good indicator of CO2ff emission.</p

HIGH-LEVEL (14)C CONTAMINATION AND RECOVERY AT XI'AN AMS CENTER

A sample with a radiocarbon concentration estimated to be greater than 10(5) times Modern was inadvertently graphitized and measured in the Xi&#39;an AMS system last year. Both the sample preparation lines and the ion source system were seriously contaminated and a series of cleaning procedures were carried out to remove the contamination from them. After repeated and careful cleaning as well as continuous flushing with dead CO(2) gas, both systems have recovered from the contamination event. The machine background is back to 2.0 x 10(-16) and the chemical blank is beyond 50 kyr.</p