  We study the environmental dependence of ultralight scalar dark matter (DM)
with linear interactions to the standard model particles. The solution to the
DM field turns out to be a sum of the cosmic harmonic oscillation term and the
local exponential fluctuation term. The amplitude of the first term depends on
the local DM density and the mass of the DM field. The second term is induced
by the local distribution of matter, such as the Earth. Then, we compute the
phase shift induced by the DM field in atom interferometers (AIs), through
solving the trajectories of atoms. Especially, the AI signal for the violation
of weak equivalence principle (WEP) caused by the DM field is calculated.
Depending on the values of the DM coupling parameters, contributions to the WEP
violation from the first and second terms of the DM field can be either
comparable or one larger than the other. Finally, we give some constraints to
DM coupling parameters using results from the terrestrial atomic WEP tests.
