We present our initial study of the electromagnetic splittings of charged and neutral mesons, and the violation of Dashens theorem. Hadron masses are calculated on MILC N_f=2+1 QCD ensembles at lattice spacing approx 0.15fm, together with quenched no
n-compact U(1) configurations. The O(a^2) tadpole improved staggered quark (asqtad) action is used both for the sea quarks and for six different valence quark masses. Chiral extrapolations are performed using partially quenched chiral perturbation theory incorporating electromagnetic corrections.
