  The New Horizons flyby of Pluto confirmed the existence of hazes in its
atmosphere. Observations of a large high- to low- phase brightness ratio,
combined with the blue color of the haze, suggest that the haze particles are
fractal aggregates, analogous to the photochemical hazes on Titan. Therefore,
studying the Pluto hazes can shed light on the similarities and differences
between the Pluto and Titan atmospheres. We model the haze distribution using
the Community Aerosol and Radiation Model for Atmospheres assuming that the
distribution is shaped by sedimentation and coagulation of particles
originating from photochemistry. Hazes composed of both purely spherical and
purely fractal aggregate particles are considered. Agreement between model
results and occultation observations is obtained with aggregate particles when
the downward flux of photochemical products is equal to the column-integrated
methane destruction rate ~1.2 $\times$ 10$^{-14}$ g cm$^{-2}$ s$^{-1}$, while
for spherical particles the mass flux must be 2-3 times greater. This flux is
nearly identical to the haze production flux of Titan previously obtained by
comparing microphysical model results to Cassini observations. The aggregate
particle radius is sensitive to particle charging, and a particle charge to
radius ratio of 30 e-/{\mu}m is necessary to produce ~0.1-0.2 {\mu}m aggregates
near Pluto's surface, in accordance with forward scattering measurements. Such
a particle charge to radius ratio is 2-4 times higher than those previously
obtained for Titan. Hazes composed of spheres with the same particle charge to
radius ratio have particles that are 4 times smaller. These results further
suggest that the haze particles are fractal aggregates. We also consider the
effect of condensation of HCN, and C$_{2}$-hydrocarbons on the haze particles,
which may play an important role in shaping their distributions.
