{\it HST}/COS Observations of the Warm Ionized Gaseous Halo of NGC 891

The metallicity of galactic gaseous halos provides insights into accretion and feedback of galaxies. The nearby edge-on galaxy NGC 891 has a multi-component gaseous halo and a background AGN (LQAC 035+042 003) projected 5 kpc above the disk near the minor axis. Against the UV continuum of this AGN, we detect lines from 13 ions associated with NGC 891 in new {\it HST}/COS spectra. Most of the absorption is from the warm ionized gas with $\log T=4.22\pm0.04$,$\log n_{\rm H}=-1.26\pm0.51$,and$\log N_{\rm H}=20.81\pm 0.20$. The metallicity of volatile elements (i.e., C, N, and S) is about half solar ($[\mathrm{X}\mathrm{/}\mathrm{H}]\approx -0.3\pm 0.3$), while Mg, Fe, and Ni show lower metallicities of $[\mathrm{X}\mathrm{/}\mathrm{H}]\approx -0.9$. The absorption system shows the depletion pattern seen for warm Galactic diffuse clouds, which is consistent with a mixture of ejected solar metallicity disk gases and the hot X-ray emitting halo ($Z=0.1-0.2Z_{\odot }$). The warm ionized gases are about 5 times more massive than the cold \ion{H}{1} emitting gases around the galactic center, which might lead to accretion with a mean rate of ${10}^2{M}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$ for a period of time. We also detect low metallicity ($\approx 0.1Z_{\odot }$) gases toward LQAC 035+042 003 at $110\mathrm{k}\mathrm{m}{\mathrm{s}}^{-1}$ (a high velocity cloud) and toward another sight line (3C 66A; 108 kpc projected from NGC 891) at $30\mathrm{k}\mathrm{m}{\mathrm{s}}^{-1}$. This low metallicity material could be the cold mode accretion from IGM or the tidal disruption of satellites in the NGC 891 halo.