# Sources of the Deposition of Submicron Soot Particles on Plant Leaves

## TL;DR

This study shows that tree leaves can track soot pollution levels and sources, finding higher soot in winter and fossil fuels as a major contributor.

## Contribution

The novel use of tree leaves and stable carbon isotopes to monitor submicron soot sources and seasonal trends.

## Key findings

- Submicron soot levels on leaves were higher in winter (0.5–1.3 mg/m²) than in summer (0.3–0.5 mg/m²).
- Fossil fuels contributed 56% of soot in winter and 78% in summer, as determined by stable carbon isotope analysis.
- Tree leaves are a cost-effective biomonitoring tool for tracking submicron soot pollution and its sources.

## Abstract

Submicron soot particles (smaller than 1.0 μm) contribute to global warming and health risks. This study analyzed soot levels on leaves from seven tree types in Nanjing, China, across four seasons over two years. The results showed higher soot levels in winter (0.5–1.3 mg/m2) compared to summer (0.3–0.5 mg/m2), with variations among tree species. Stable carbon isotope analysis revealed that fossil fuels were the primary source, contributing 56% in winter and 78% in summer. The findings suggest tree leaves can be a cost-effective tool for monitoring submicron soot pollution and its sources.

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.