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

Abstract

Independent identification of carbon emission peaks determined from fuel inventories is a challenging goal. Because of the complete depletion of radiocarbon (¹⁴C) in fossil fuel sources, the measurement of atmospheric ¹⁴CO₂ 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 Δ¹⁴C time series during 2000–2019. After subtracting background atmospheric Δ¹⁴C from urban tree-ring Δ¹⁴C to isolate local Δ¹⁴C (Δ¹⁴C_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 Δ¹⁴C 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.