= Solution
For the stated total number density, multiply the number <atmospheric mixing ratio> by $[\mathrm M]$. With NO$_x$ defined as NO plus NO$_2$,
$$
\boxed{\begin{aligned}
[\mathrm{NO_x}]&=2.46\times10^{11},&[\mathrm{NO}]&=7.38\times10^{10},\\
[\mathrm{NO_2}]&=1.722\times10^{11},&[\mathrm O_3]&=9.84\times10^{11},\\
[\mathrm{H_2O}]&=7.38\times10^{17}
\end{aligned}\quad\mathrm{molecules\,cm^{-3}}}.
$$
The <water> partial <pressure> is $30/1000=0.030$ of the total <pressure>. It is a 3% number fraction, not 30 ppm.
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