  We propose a very simple physical mechanism responsible for the formation of
the Low Ionization Line part of the Broad Line Region in Active Galactic
Nuclei. It explains the scaling of the Broad Line Region size with the
monochromatic luminosity, including the exact slope and the proportionality
constant, seen in the reverberation studies of nearby sources. The scaling is
independent from the mass and accretion rate of an active nucleus. The
mechanism predicts the formation of a dust-driven wind in the disk region where
the local effective temperature of a non-illuminated accretion disk drops below
1000 K and allows for dust formation. We explore now the predictive power of
the model with the aim to differentiate between this model and the previously
proposed mechanisms of the formation of the Broad Line Region. We discuss the
expected departures from the universal scaling at long wavelength, and the role
of the inclination angle of the accretion disk in the source. We compare the
expected line profiles with Mg II line profiles in the quasars observed by us
with the SALT telescope. We also discuss the tests based on the presence or
absence of the broad emission lines in low luminosity active galaxies. Finally,
we discuss the future tests of the model to be done with expected ground-based
observations and satellite missions.
