The elemental and isotopic composition of sulfur and nitrogen in Chinese coals

Coal combustion is an important atmospheric pollution source in most Chinese cities, so systematic studies on sulfur and nitrogen in Chinese coals are needed. The sulfur contents in Chinese coals average 0.9 ± 1.0%, indicating that most Chinese coals are low in sulfur. A nearly constant mean δ34S value is observed in low sulfur (TS < 1) Chinese coals of different ages (D, P1, T3 and J3). High sulfur Chinese coals (OS > 0.8%), often found at late Carboniferous (C3) and late Permian (P2) in southern China, had two main sulfur sources (original plant sulfur and secondary sulfur). The wide variety of δ34S values of Chinese coals (−15‰ to +50‰) is a result of a complex sulfur origin. The δ15N values of Chinese coals ranged from −6‰ to +4‰, showing a lack of correlation with coal ages, whereas nitrogen contents are higher in Paleozoic coals than in Mesozoic coals. This may be related to their original precursor plant species: high nitrogen pteridophytes for the Paleozoic coals and low nitrogen gymnosperms for the Mesozoic coals. Different to δ34S values, Chinese coals showed higher δ15N values in marine environments than in freshwater environments.