  The C/O ratio is a defining feature of both gas giant atmospheric and
protoplanetary disk chemistry. In disks, the C/O ratio is regulated by the
presence of snowlines of major volatiles at different distances from the
central star. We explore the effect of radial drift of solids and viscous gas
accretion onto the central star on the snowline locations of the main C and O
carriers in a protoplanetary disk, H2O, CO2 and CO, and their consequences for
the C/O ratio in gas and dust throughout the disk. We determine the snowline
locations for a range of fixed initial particle sizes and disk types. For our
fiducial disk model, we find that grains with sizes ~0.5 cm < s < 7 m for an
irradiated disk, and ~0.001 cm < s < 7 m for an evolving and viscous disk,
desorb at a size-dependent location in the disk, which is independent of the
particle's initial position. The snowline radius decreases for larger
particles, up to sizes of ~7 m. Compared to a static disk, we find that radial
drift and gas accretion in a viscous disk move the H2O snowline inwards by up
to 40%, the CO2 snowline by up to 60%, and the CO snowline by up to 50%. We
thus determine an inner limit on the snowline locations when radial drift and
gas accretion are accounted for.
