  We investigate particle spectra and elliptic flow coefficients in
relativistic heavy ion collisions by taking into account the distortion of
phase space distributions due to bulk viscosity at freezeout. We first
calculate the distortion of phase space distributions in a multi-component
system within the Grad's fourteen moment method. We find some subtle issues
when one matches macroscopic variables with microscopic momentum distributions
in a multi-component system and develop a consistent procedure to uniquely
determine the corrections in the phase space distributions. Next, we calculate
particle spectra by using the Cooper-Frye formula to see the effect of the bulk
viscosity. In spite of the relative smallness of the bulk viscosity, we find
that it is likely to have a visible effect in particle spectra and elliptic
flow coefficients. This indicates the importance of bulk viscosity together
with shear viscosity if one wants to constrain the transport coefficients with
better accuracy from experimental data.
