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\bibitem{Ravindra_etal2006} {\textquotedblleft}\textit{Assessment of air quality after the implementation of Compressed Natural Gas (CNG) as fuel in public transport in Delhi, India}{\textquotedblright}. Ravindra K, Wauters E, Tyagi SK, Mor S, Van Grieken R, Environmental monitoring and assessment \textbf{115}, 405 (2006).   http://doi.org/10.1007/S10661-006-7051-5

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