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\bibitem{Leysen_etal1987} {\textquotedblleft}\textit{Classification of suspended particles in deposition samples and run-off water samples from a limestone cathedral}{\textquotedblright}. Leysen LA, Roekens EJ, Storms H, Van Grieken RE, Atmospheric environment \textbf{21}, 2425 (1987).   http://doi.org/10.1016/0004-6981(87)90377-5

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