  We numerically investigate abundance properties of the Galactic globular
clusters (GCs) by adopting a new ``external pollution'' scenario. In this
framework, GCs are assumed to originate in forming low-mass dwarfs embedded in
dark matter subhalos at very high redshifts (z) and thus be chemically
influenced by field AGB stars of the dwarfs during early GC formation
processes. In this external pollution scenario, the ratio of the total mass of
infalling gas to that of AGB ejecta during GC formation in a dwarf (s) and the
time scale of gas infall (sigma_I) are the most important key parameters that
can determine abundance properties of GCs. We mainly investigate the abundance
inhomogeneity among light elements (e.g., C, N, O, Na, and Al) of stars in GCs
by using the latest stellar yield models of metal-poor AGB stars with and
without third dredge-up. Our principal results for the models with no third
dredge-up, which are more consistent with observations, are as follows.
  Both [N/Fe] and [C/Fe] can be diverse among stars within a GC owing to
chemical pollution from field AGB stars. [N/Fe] distributions in some GCs can
clearly show bimodality whereas [C/Fe] is monomodal in most models. [N/Fe]
distributions depend on s such that models with smaller $s$ (i.e., larger mass
fraction of AGB ejecta used for GC formation) show the [N/Fe] bimodality more
clearly. N-rich, C-poor stars in GCs also have higher He abundances owing to
pollution from massive AGB stars with He-rich ejecta. The number fraction of
He-rich stars (Y >0.30) is higher for the models with smaller s and shorter
sigma_I for 3 < s <24 and 10^5 < sigma_I < 10^7 yr.Our models are in strong
disagreement with the observed O-Na anticorrelation.
