Identification of Urban Carbon Emission Peaks through Tree-Ring 14 C.

Independent identification of carbon emission peaks determined from fuel inventories is a challenging goal. Because of the complete depletion of radiocarbon ( 14 C) in fossil fuel sources, the measurement of atmospheric 14 CO 2 has proven to offer a means of achieving this goal. Here, we present a study identifying peak carbon emissions from two Chinese cities using urban tree-ring Δ 14 C time series during 2000-2019. After subtracting background atmospheric Δ 14 C from urban tree-ring Δ 14 C to isolate local Δ 14 C (Δ 14 C local ), we find a minimum in 2010 (-51.1 ± 4.5‰) in Beijing and in 2013 in Xi'an (-52.5 ± 0.5‰). These levels correspond to an urban carbon emission peak in 2010 and in 2013 in the two respective cities. The urban carbon emission peaks are further identified by the declines of the mean absolute interannual rate of decrease of tree-ring Δ 14 C during a period, with the respective values of 3.6 and 6.4 ‰/yr after and before a turning point in Beijing and 3.0 and 6.0 ‰/yr after and before a turning point in Xi'an. This study provides an observation method to identify carbon emission peaks in basin cities.