  We present one-dimensional non-local thermodynamic equilibrium time-dependent
radiative transfer simulations (using CMFGEN) of two sub-Chandrasekhar
(sub-$M_{\rm Ch}$), one $M_{\rm Ch}$ and one super-$M_{\rm Ch}$ Type Ia SN
ejecta models. Three originate from $M_{\rm Ch}$ delayed detonation models, and
the fourth is a sub-$M_{\rm Ch}$ detonation model. Ejecta masses are 1.02,
1.04, 1.40, and 1.70 M$_\odot$, and all models have 0.62 M$_\odot$ of
$^{56}{\rm Ni}$. Sub-$M_{\rm Ch}$ model light curves evolve faster, reaching
bolometric maximum 2--3 days earlier and having 3--4 days shorter bolometric
half light widths. The models vary by $\sim$12 per cent at maximum bolometric
luminosity and by 0.17 mag in $B_{\rm max}$. While $\Delta M_{15}(B)$ increases
with ejecta mass it only varies by $\sim$5 per cent around 1 mag. Sub-$M_{\rm
Ch}$ models are 0.25 mag bluer in $B-R$ at $B_{\rm max}$. Optical spectra share
many similarities, but lower mass models exhibit less UV line blanketing during
the photospheric phase. At nebular times, significant NIR spectroscopic
differences are seen. In particular, emission lines of the Ca II NIR triplet;
[S III] $\lambda\lambda$9068,9530; [Ca II] $\lambda\lambda$7291,7324; [Ar III]
$\lambda\lambda$7135,7751; and [Ni II] 1.939 $\mu$m are stronger in higher mass
models. The [Ni II] 1.939 $\mu$m line is absent in the sub-$M_{\rm Ch}$
detonation model, and provides a valuable potential tool to distinguish
sub-$M_{\rm Ch}$ explosions from $M_{\rm Ch}$ explosions. In general, the
nebular phase models are too highly ionized. We attribute this to the neglect
of clumping and/or the distribution of intermediate mass and iron group
elements. The two sub-$M_{\rm Ch}$ models, while exploded by different
mechanisms, can be distinguished in the $J$ and $H$ bands at late times (e.g.,
$+200$ days).
