upright mus (greek letter in general) in latex

microgram.tex

\documentclass{minimal}
\usepackage{siunitx}
\usepackage[sc]{mathpazo}
\linespread{1.05}         % Palatino needs more leading (space between lines)
\usepackage[T1]{fontenc}
\begin{document}
who wins?
\si{\micro\gram\per\liter}  vs. $\mu$g/L
\end{document}