Stable carbon isotopic characteristics of fossil fuels in China.

Good knowledge on the stable carbon isotopic composition (δC) of fossil fuels is critical for the estimation of atmospheric CO sources. Here, we complied a comprehensive δC 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 δC signatures of Chinese fossil fuels. Results show that coal exhibits a narrow range and the most enriched in δC signature, oil displays intermediate variations both in the distribution and value of δC. By contrast, natural gas is strongly depleted but became more enriched in δC 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 δC 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 δC of fossil fuels is used to estimate CO source contributions, and the measurement of δCO 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 CO sources of fossil fuel emissions in China, and also make a contribute to the global carbon isotope database.