Optical/UV radiation from accretion discs in quasars are likely to be
partly scattered by a hot plasma enveloping the disc. It has been
investigated whether the scattering may produce the mysterious steep rises
in polarization observed blueward of the Lyman limit in some quasars. Two
models have been suggested and assessed:
i) The primary
disc radiation with a Lyman edge in absorption passes through a static
ionized ``skin'' covering the disc, which has a Thomson optical depth
. Electron scattering in the skin smears out the edge and
produces a steep rise in polarization at 
Å.
ii) The scattering occurs in a hot coronal plasma outflowing from
the disc with a mildly relativistic velocity. The second model better
explains the rise in polarization. Presently, the outflow model is the
only known model reproducing successfully the whole pattern of polarization
in non-blazar AGNs from the optical to the UV.