C-AMS measurements in modern tree rings to trace local fossil fuel-derived CO in the greater Xi'an area, China.

Fossil fuel-derived CO (CO) time series are critical to understanding urban carbon emissions, and to devise strategies to mitigate emission reduction. Using tree ring C archives, we reconstruct an historical CO time series from 1991 to 2015 in the greater Xi'an region, China. CO concentrations from the urban sites reached 22.5 ppm, with an average of 14.0 ppm, while average values from rural and mountain sites averaged about 6.0 ppm. These values provide a good measure of the distribution of anthropogenic CO emissions in the region. We also observed CO concentration increases from both urban and rural sites during the study period, with more significant increases among urban sites. The persistent rise in CO was attributed to increasing energy consumption caused by regional socio-economic development, which are corroborated by strong correlations between CO and socioeconomic parameters.