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.