Stable carbon isotopic characteristics of fossil fuels in China

Good knowledge on the stable carbon isotopic composition (δ13C) of fossil fuels is critical for the estimation of atmospheric CO2 sources. Here, we complied a comprehensive δ13C database including 336 coal, 580 oil, and 1160 natural gas data based on the extensive literature search, and conducted field measurements in two megacities, to characterize the δ13C signatures of Chinese fossil fuels. Results show that coal exhibits a narrow range and the most enriched in δ13C signature, oil displays intermediate variations both in the distribution and value of δ13C. By contrast, natural gas is strongly depleted but became more enriched in δ13C signature due to the shift in production from isotopically light oil-type gas to isotopically heavy coal-type gas. We found an obvious overlap between the δ13C distributions of oil and natural gas, and the carbon isotopic difference between oil and natural gas is minimized in Ordos Basin. Therefore, we suggested that the geographic origin is a certain factor that must be considered when δ13C of fossil fuels is used to estimate CO2 source contributions, and the measurement of δ13CO2 signatures of local end members is a better alternative in the absence of detailed information about the geographical origins of fossil fuels. This work is helpful in improving the ability to quantify CO2 sources of fossil fuel emissions in China, and also make a contribute to the global carbon isotope database. [Display omitted] •Updated δ13C database of Chinese fossil fuel was compiled based on more than 2000 literature data.•Natural gas became enriched in δ13C signature due to the increased production of coal-type gas.•There is a significant overlap between the δ13C distributions of oil and natural gas.•The applicability of the database and necessity of field measurements are introduced.