Identification of\nUrban Carbon Emission Peaks through\nTree-Ring <sup>14</sup>C

Independent identification of carbon emission peaks determined\nfrom fuel inventories is a challenging goal. Because of the complete\ndepletion of radiocarbon (<sup>14</sup>C) in fossil fuel sources,\nthe measurement of atmospheric <sup>14</sup>CO<sub>2</sub> has proven\nto offer a means of achieving this goal. Here, we present a study\nidentifying peak carbon emissions from two Chinese cities using urban\ntree-ring Δ<sup>14</sup>C time series during 2000–2019.\nAfter subtracting background atmospheric Δ<sup>14</sup>C from\nurban tree-ring Δ<sup>14</sup>C to isolate local Δ<sup>14</sup>C (Δ<sup>14</sup>C<sub>local</sub>), we find a minimum\nin 2010 (−51.1 ± 4.5‰) in Beijing and in 2013 in\nXi’an (−52.5 ± 0.5‰). These levels correspond\nto an urban carbon emission peak in 2010 and in 2013 in the two respective\ncities. The urban carbon emission peaks are further identified by\nthe declines of the mean absolute interannual rate of decrease of\ntree-ring Δ<sup>14</sup>C during a period, with the respective\nvalues of 3.6 and 6.4 ‰/yr after and before a turning point\nin Beijing and 3.0 and 6.0 ‰/yr after and before a turning\npoint in Xi’an. This study provides an observation method to\nidentify carbon emission peaks in basin cities.