Observations of atmospheric Δ¹⁴CO₂ at the global and regional background sites in China: Implication for fossil fuel CO₂ inputs

Six months to more than one year of atmospheric Δ¹⁴CO₂ were measured in 2014-2015 at one global background site in Waliguan (WLG) and four regional background sites at Shangdianzi (SDZ), Lin'an (LAN), Longfengshan (LFS) and Luhuitou (LHT), China. The objectives of the study are to document the Δ¹⁴CO₂ levels at each site and to trace the variations in fossil fuel CO₂ (CO_2ff) inputs at regional background sites. Δ¹⁴CO₂ at WLG varied from 7.1 ± 2.9‰ to 32.0 ± 3.2‰ (average 17.1 ± 6.8‰) in 2015, with high values generally in autumn/summer and low values in winter/spring. During the same period, Δ¹⁴CO₂ values at the regional background sites were found to be significantly (p < 0.05) lower than those at WLG, indicating different levels of CO_2ff inputs at those sites. CO_2ff concentrations at LAN (12.7 ± 9.6 ppm) and SDZ (11.5 ± 8.2 ppm) were significantly (p < 0.05) higher than those at LHT (4.6 ± 4.3 ppm) in 2015. There were no significant (p > 0.05) seasonal differences in CO_2ff concentrations for the regional sites. Regional sources contributed in part to the CO_2ff inputs at LAN and SDZ, while local sources dominated the trend observed at LHT. These data provide a preliminary understanding of atmospheric Δ¹⁴CO₂ and CO_2ff inputs for a range of Chinese background sites.