  The processes that govern the evolution of dust and water (in the form of
vapor or ice) in protoplanetary disks are intimately connected. We have
developed a model that simulates dust coagulation, dust dynamics (settling,
turbulent mixing), vapor diffusion, and condensation/sublimation of volatiles
onto grains in a vertical column of a protoplanetary disk. We employ the model
to study how dust growth and dynamics influence the vertical distribution of
water vapor and water ice in the region just outside the radial snowline. Our
main finding is that coagulation (boosted by the enhanced stickiness of icy
grains) and the ensuing vertical settling of solids results in water vapor
being depleted, but not totally removed, from the region above the snowline on
a timescale commensurate with the vertical turbulent mixing timescale.
Depending on the strength of the turbulence and the temperature, the depletion
can reach factors of up to ${\sim}50$ in the disk atmosphere. In our isothermal
column, this vapor depletion results in the vertical snowline moving closer to
the midplane (by up to 2 gas scale heights) and the gas-phase C/O ratio above
the vertical snowline increasing. Our findings illustrate the importance of
dynamical effects and the need for understanding coevolutionary dynamics of gas
and solids in planet-forming environments.
