Let the real numbers $a_{1}, a_{2}, \ldots, a_{9}$ form an arithmetic sequence with common difference 2, where $a_{1} \neq 0$ and $a_{3} > 0$. If $\log_{2} a_{3}$, $\log_{2} b$, $\log_{2} a_{9}$ form an arithmetic sequence in order, where $b$ is one of $a_{4}, a_{5}, a_{6}, a_{7}, a_{8}$, then $a_{9} = $ \underline{\hspace{2cm}}.\\
(Express as a simplified fraction)