  In recent years many models of chondrule formation have been proposed. One of
those models is the processing of dust in shock waves in protoplanetary disks.
In this model, the dust and the chondrule precursors are overrun by shock
waves, which heat them up by frictional heating and thermal exchange with the
gas. In this paper we reanalyze the nebular shock model of chondrule formation
and focus on the downstream boundary condition. We show that for large-scale
plane-parallel chondrule-melting shocks the postshock equilibrium temperature
is too high to avoid volatile loss. Even if we include radiative cooling in
lateral directions out of the disk plane into our model (thereby breaking
strict plane-parallel geometry) we find that for a realistic vertical extent of
the solar nebula disk the temperature decline is not fast enough. On the other
hand, if we assume that the shock is entirely optically thin so that particles
can radiate freely, the cooling rates are too high to produce the observed
chondrules textures. Global nebular shocks are therefore problematic as the
primary sources of chondrules.
