Progress of Tracing Fossil Fuel CO2 by Radiocarbon in Chinese Cities

The main cause of increase in atmospheric CO₂ concentration is the carbon emissions from fossil fuel combustions and so on. Cities are regarded as the hot spots of carbon emissions. On the basis of obtaining the levels and spatial-temporal variation characteristics of atmospheric fossil fuel CO₂ （CO_2ff）， we can provide scientific data for government policy-making and international negotiations on carbon reductions. In the recent ten years， some important progresses have been achieved in the study of tracing urban atmospheric CO_2ff using ¹⁴C by Chinese scientists. The variation characteristics of urban CO_2ff at different temporal and spatial scales were obtained through the analysis of ¹⁴C in air， tree ring and annual plant samples. Our results show that the northern cities are the key points to reduce carbon emissions， and that the CO_2ff emissions can be reduced simultaneously by controlling atmospheric pollutant emissions， indicating a synergistic emission reduction. It was found that CO_2ff in Xi'an was mainly from local coal-burning emissions with the use of improved WRF-CHEM model and δ¹³C. Finally， the yearly CO_2ff traced by tree-ring ¹⁴C in Xi'an showed similar trends and amplitudes with the statistical data of carbon emissions， which indicates that the ¹⁴C tracing method and statistical method can be mutually validated to ensure the reliability of the data. In order to promote the ¹⁴C trace study to serve the national carbon emission reduction task， we suggest that the urban atmospheric Δ¹⁴CO₂ observation network should be established as soon as possible， and that this study should be enhanced with more scientists involved in it and more financial resources to support it.