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\bibitem{Eltayeb_etal1992} {\textquotedblleft}\textit{Size-differentiated composition of aerosols in Khartoum, Sudan}{\textquotedblright}. Eltayeb MAH, van Espen PJ, Cafmeyer J, Van Grieken RE, Maenhaut W, The science of the total environment \textbf{120}, 281 (1992).   http://doi.org/10.1016/0048-9697(92)90062-W

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