%&LaTeX
\documentclass{article}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{textcomp}

\begin{document}

\begin{thebibliography}{1}

\bibitem{Rojas_etal1989} {\textquotedblleft}\textit{Characterization of airborne particulate matter collected over the North Sea}{\textquotedblright}. Rojas CM, Otten PM, Van Grieken RE, Journal of aerosol science \textbf{20}, 1257 (1989).   http://doi.org/10.1016/0021-8502(89)90811-2

\end{thebibliography}

\end{document}

