Assessing atmospheric dry deposition via water-soluble ionic composition of roadside leaves

Abstract

This study focuses on the water-soluble ion concentrations in the washing solution of leaves of different roadside tree species at three sites in Iran to estimate the ionic composition of the dry deposition of ambient air particulates. All considered water-soluble ion concentrations were significantly higher next to the roads with high traffic density compared to the reference site with low traffic density. The PCA results showed that Ca²⁺, Mg²⁺, ${NO}_3^{-}$ and ${SO}_4^{2-}$ originated mainly from traffic activities and geological sources, and Na⁺, Cl⁻, K⁺ and F⁻ from sea salts. In addition to sea salt, K⁺ and F⁻ were also originated from anthropogenic sources i.e. industrial activities, biomass burning and fluorite mining. Moreover, the concentration of the water-soluble ions depended on species and site. C. lawsoniana had significantly higher ion concentrations in its leaf washing solution compared to L. japonicum and P. brutia which indicates C. lawsoniana is the most suitable species for accumulating of atmospheric dry deposition. From our results, it can be concluded that sites with similar traffic density can have different particle loads and water-soluble ion species, and that concentrations in leaf-washing solutions depend on site conditions and species-specific leaf surface characteristics.

Keywords:

• Atmospheric particles
• road traffic
• urban tree
• monitoring
• air pollution
• species specific
• nitrate
• sulfate
• chloride
• principal component analysis

Acknowledgments

Authors thank Barbara Krupinska for lab assistance at the University of Antwerp, Belgium. Also, we thank Prof. Dr. Alireza Naqinezhad for tree species identification at the University of Mazandaran, Iran. Also, we thank the National Iranian Oil Company and Tehran air quality agency for the information provided.