We study the dust concentration and emission in protoplanetary disks vortices .
We extend the Lyra-Lin solution for the dust concentration of a single grain size to a power-law distribution of grain sizes n ( a ) \propto a ^ { - p } .
Assuming dust conservation in the disk , we find an analytic dust surface density as a function of the grain radius .
We calculate the increase of the dust to gas mass ratio \epsilon and the slope p of the dust size distribution due to grain segregation within the vortex .
We apply this model to a numerical simulation of a disk containing a persistent vortex .
Due to the accumulation of large grains towards the vortex center , \epsilon increases by a factor of 10 from the background disk value , and p decreases from 3.5 to 3.0 .
We find the disk emission at millimeter wavelengths corresponding to synthetic observations with ALMA and VLA .
The simulated maps at 7 mm and 1 cm show a strong azimuthal asymmetry .
This happens because , at these wavelengths , the disk becomes optically thin while the vortex remains optically thick .
The large vortex opacity is mainly due to an increase in the dust to gas mass ratio .
In addition , the change in the slope of the dust size distribution increases the opacity by a factor of 2 .
We also show that the inclusion of the dust scattering opacity substantially changes the disks images .