Standard deviation for the particulate matter (PM) concentrations listed in the table is $\_\_\_\_$ $\mu \mathrm{g} / \mathrm{m}^{3}$ (rounded off to one decimal place).
$$\begin{array}{|l|c|c|c|c|c|c|c|}
\hline
\textbf{Location No.} & 1 & 2 & 3 & 4 & 5 & 6 & 7 \\
\hline
\begin{array}{l}
\textbf{PM concentration} \\
(\mu \mathrm{g}/\mathrm{m}^{3})
\end{array}
& 45 & 40 & 55 & 65 & 60 & 35 & 50 \\
\hline
\end{array}$$
