  It is shown that clustering of charged impurities on graphene can suppress
their contribution to the resistivity by a large factor of about the number of
impurities per cluster, while leaving the density dependence unchanged. If the
cluster size is large in comparison with the Fermi wavelength, the scattering
cross section shows sharp resonances as a function of incident angle and
electron wavevector. In this regime, due to dominant contribution of scattering
by small angles, the transport cross section can be much smaller than the
quantum one, which can be verified experimentally by comparing the Dingle
temperature and the electron mean free path.
