Elemental carbon components and PAHs in soils from different areas of the Yangtze River Delta region, China and their relationship

Elemental carbon (EC) is a chemically heterogeneous class of carbonaceous particles-including char, soot, coke, charcoal, and others-that form by incomplete fossil fuel and biomass combustion. Many previous studies indicate that EC has a better correlation with polycyclic aromatic hydrocarbon (PAH) distribution in urban soils than total organic carbon (TOC). Nevertheless, the correlation between EC components and PAHs in developed regions is still not clear. Accordingly, we explored the concentrations, sources, and correlations of EC components with PAHs in soils from different areas of the Yangtze River Delta region, China. The results showed that soil EC and PAH levels were higher in Nanjing (high urbanization) than in Dingshu or Lujia (lower urbanization), yet TOC exhibited the opposite trend with respect to PAH levels. The main sources of both EC and PAHs were fossil fuel and biomass combustion, but there were differences between the study areas. The Sigma(16)PAHs concentration was strongly associated with char-EC and soot-EC levels in Nanjing (P < 0.01), yet was only strongly associated with char-EC level in Dingshu (P < 0.01). We found no significant correlations between the concentrations of PAHs and any carbon component in Lujia (P > 0.05), mainly due to the relatively low EC and PAH levels in these rural samples. Based on our results, we built quantitative equations that describe the relationships between the concentrations of PAHs and specific carbon types. Moreover, we also constructed a quantitative relationship model of soil PAH distribution association with urbanization indicators, soil properties, and other factors. Our findings will help researchers deeply understand the formation mechanism of PAHs in urban soils.