  Different scattering mechanisms in graphene are explored and conductivity is
calculated within the Boltzmann transport theory. We provide results for
short-range scattering using the Random Phase Approximation for electron
screening, as well as analytical expressions for the dependence of conductivity
on the dielectric constant of the substrate. We further examine the effect of
ripples on the transport using a surface roughness model developed for
semiconductor heterostructures. We find that close to the Dirac point, \sigma
\sim n^\beta, where \beta=1,0,-2 for Coulomb, short-range and surface roughness
respectively; implying that Coulomb scattering dominates over both short-range
and surface roughness scattering at low density.
