[Soil record of black carbon during urbanization and its environmental implications].
This investigation selected the city of Nanjing, Jiangsu province of China, as the study area, and analyzed the concentrations of organic carbon (OC) and black carbon (BC) of ten soils profiles in three different groups, by wet chemical oxidation methods. The results showed that the concentration of BC ranged from 0.22 g x kg(-1) to 32.19 g x kg(-1) in all urban soil profiles, and the average concentration of BC reached 4.35 g x kg(-1). The average concentration of BC of the first group from ancient residential areas was 0.91 g x kg(-1), and that of the second group affected by ancient industrial activities was 8.62 g x kg(-1), the third group influenced by the modern industrial and traffic emission was 3.72 g x kg(-1). The ratio of BC/OC ranged from 0.03 to 1.59 in all profiles, and the average was 0.29. The average ratio of BC/OC of three groups appeared in this order: the highest exists in the second group, followed by the third group, and the last is the first group. These data mean that some BC particles produced by local biomass and/or fossil fuel burning due to the industrial and transport activities during urbanization are recorded in soils. In addition, the contents of BC and the ratio of BC/OC may reflect different processes of human activities and pollution intensities of urban soils. It is concluded that the soil BC in urban area is mainly coming from fossil fuel burning, more specifically, BC in surface layer (present layer) is mainly from the exhaust particles of motor vehicles (especially diesel engine), while in ancient layer (cultural layer) it is possibly related to the historical coal use.