  We present results of 2.5D numerical simulations of the emergence of
sub-surface magnetic flux into the solar atmosphere, with emerging flux regions
ranging from $10^{18}$ to $10^{21}$ Mx, representing both ephemeral and active
regions. We include the presence of neutral Hydrogen in the governing
equations, improve upon previous models by including the ionization in the
equation of state, and use a more realistic convection zone model. We find that
ionization and recombination of plasma during the rise of a convection zone
flux tube reduces the rise speed of the tube's axis. The presence of neutral
Hydrogen allows the effective flow of mass across fieldlines, by the addition
of a Pedersen resistivity to the generalized Ohm's law, which dissipates
current perpendicular to the magnetic field. This causes an increase of up to
10% in the amount of magnetic in-plane flux supplied to the corona and a
reduction of up to 89% in the amount of sub-surface plasma brought up into the
corona. However, it also reduces the amount of free magnetic energy supplied to
the corona, and thus does not positively affect the likelihood of creating
unstable coronal structures.
