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The repeating FRB 20190520B is localized to a galaxy at $z=0.241$, muchcloser than expected given its dispersion measure $\rm DM=1205\pm4\ pc\cm^{-3}$. Here we assess implications of the large DM and scattering observedfrom FRB 20190520B for the host galaxy's plasma properties. A sample of 75bursts detected with the Five-hundred-meter Aperture Spherical radio Telescopeshows scattering on two scales: a mean temporal delay $\tau(1.41\ {\rmGHz})=10.9\pm1.5$ ms, which is attributed to the host galaxy, and a meanscintillation bandwidth $\nu_{\rm d}(1.41\ {\rm GHz})=0.21\pm0.01$ MHz, whichis attributed to the Milky Way. Balmer line measurements for the host imply anH$\alpha$ emission measure (galaxy frame) $\rm EM_s=620$ pc cm$^{-6} \times(T/10^4 {\rm K})^{0.9}$, implying $\rm DM_{\rm H\alpha}$ of order the valueinferred from the FRB DM budget, $\rm DM_h=1121^{+89}_{-138}$ pc cm$^{-3}$ forplasma temperatures greater than the typical value $10^4$ K. Combining $\tau$and $\rm DM_h$ yields a nominal constraint on the scattering amplification fromthe host galaxy $\tilde{F} G=1.5^{+0.8}_{-0.3}$ (pc$^2$ km)$^{-1/3}$, where$\tilde{F}$ describes turbulent density fluctuations and $G$ represents thegeometric leverage to scattering that depends on the location of the scatteringmaterial. For a two-screen scattering geometry where $\tau$ arises from thehost galaxy and $\Delta \nu_{\rm d}$ from the Milky Way, the implied distancebetween the FRB source and dominant scattering material is $\lesssim100$ pc.The host galaxy scattering and DM contributions support a novel technique forestimating FRB redshifts using the $\tau-\rm DM$ relation, and are consistentwith previous findings that scattering of localized FRBs is largely dominatedby plasma within host galaxies and the Milky Way.

The Large Dispersion and Scattering of FRB 20190520B are Dominated by the Host Galaxy