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\bibitem{Alejo_etal2013} {\textquotedblleft}\textit{Seasonal trends of atmospheric nitrogen dioxide and sulfur dioxide over North Santa Clara, Cuba}{\textquotedblright}. Alejo D, Morales MC, de la Torre JB, Grau R, Bencs L, Van Grieken R, van Espen P, Sosa D, Nu{\~n}ez V, Environmental monitoring and assessment \textbf{185}, 6023 (2013).   http://doi.org/10.1007/S10661-012-3003-4

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