Sources of the Deposition of Submicron Soot Particles on Plant Leaves

Submicron soot particles (with an aerodynamic diameter of less than 1.0 μm) are found to be one of the major factors resulting in global warming and health burdens. However, research on the biomonitoring of submicron soot particles and their associated sources using tree leaves has not been comprehensively conducted. This study investigated the seasonal trends of submicron soot particles on the leaves of seven tree types collected from four individual seasons across two years in Nanjing, in the Yangtze River Delta region of China, and performed source apportionment using stable carbon isotope analysis. Significant seasonal variations in submicron soot particles were observed on tree leaves of seven tree types, with average levels of 0.3 to 0.5 mg m^-2 during summer and 0.5 to 1.3 mg m^-2 during winter. The levels of submicron soot particles varied significantly across various tree types. In contrast, the levels of δ¹³C were not found to change significantly across different types. The levels of δ¹³C ranged from -26.3‱ to -20.9‱ in winter and from -24.0‱ to -18.1‱ in summer, with fossil fuels accounting for 56% and 78% of submicron soot in winter and summer on average, respectively. These results demonstrate that tree leaves can serve as a low-cost and effective biomonitoring tool for assessing the source status of submicron soot.