  We investigate the chemical evolution of complex organic molecules (COMs) in
turbulent disks using gas-ice chemical reaction network simulations. We trace
trajectories of dust particles considering advection, turbulent diffusion, gas
drag, and vertical settling, for 10$^6$ yrs in a protoplanetary disk. Then, we
solve a gas-ice chemical reaction network along the trajectories and obtain the
temporal evolution of molecular abundances. We find that the COM abundances in
particles can differ by more than two orders of magnitude even when the UV
fluence (i.e., the time integral of UV flux) received by the particles are
similar, suggesting that not only the UV fluence but also the time variation of
the UV flux does matter for the evolution of COMs in disks. The impact of UV
fluence on molecular abundances differs between oxygen-bearing and
nitrogen-bearing COMs. While higher UV fluence results in oxygen being locked
into CO$_2$, leading to reduced abundances of oxygen-bearing COMs such as
CH$_3$OCH$_3$, mild UV exposure can promote their formation by supplying the
precursor radicals. On the other hand, nitrogen is not locked up into specific
molecules, allowing the formation of nitrogen-bearing COMs, particularly
CH$_3$NH$_2$, even for the particle that receives the higher UV fluence. We
also find that the final COM abundances are mostly determined by the inherited
abundances from the protostellar core when the UV fluence received by dust
particles is less than a critical value, while they are set by both the
inherited abundances and the chemistry inside the disk at higher UV fluence.
