\documentclass{article}
\usepackage{siunitx}
\begin{document}
\qty{4}{\angstrom}
\end{document}
但是要说明的是, 这个符号已经不在国际单位制中了, 在以后的版本中可能需要手动添加
Unit macro \angstrom has been deprecated in this
(siunitx) release.
(siunitx)
(siunitx) The BIPM have removed this unit from the SI Brochure.
(siunitx) You should define it yourself using \DeclareSIUnit in
(siunitx) your source. The current definition is
(siunitx)
(siunitx) \DeclareSIUnit\angstrom{\text {Å}}