  We study the long-term radial transport of micron to mm-size grain in
protostellar disks (PSDs) based on diffusion and viscosity coefficients
measured from 3D global stratified-disk simulations with a Lagrangian
hydrodynamic method. While gas-drag tend to transport dust species radially
inwards, stochastic diffusion can spread a considerable fraction of dust
radially outwards (upstream) depending on the nature of turbulence. In
gravitationally unstable disks, we measure a high radial diffusion coefficient
Dr with little dependence on altitude. This leads to strong and vertically
homogeneous upstream diffusion in early PSDs. In the solar nebula, the robust
upstream diffusion of micron to mm size grains not only efficiently transports
highly refractory mocron-size grains (such as those identified in the samples
of comet 81P/Wild 2) from their regions of formation inside the snow line out
to the Kuiper Belt, but can also spread mm-size CAI formed in the stellar
proximity to distances where they can be assimilated into chondritic
meteorites. In disks dominated by magnetorotational instability (MRI), the
upstream diffusion effect is generally milder, with a separating feature due to
diffusion being stronger in the surface layer than the midplane. This variation
becomes much more pronounced if we additionally consider a quiescent midplane
with lower turbulence and larger characteristic dust size due to non-ideal MHD
effects. This segregation scenario helps to account for dichotomy of two dust
populations' spatial distribution as observed in scattered light and ALMA
images.
