Abundances of Ne, S, Ar, and O as a function of distance from the Galactic centre. The bulge PNe (squares) do not have known distances but those with high velocity are all between 0 and 3 kpc from the centre. For some of these PNe the distance listed by Gutenkunst et al. (2008) is used to avoid crowding of the points. The red and blue symbols indicate the solar abundances and the average bulge abundances respectively. The filled circles in the oxygen diagram indicate those PNe where oxygen burning is thought to have taken place.