Fig. 2a-d. Density, temperature, and abundance profiles for NGC 2440, NGC 2818, NGC 2899, and NGC 6072. and are indicated by filled and open circles, respectively. Symbols are plotted slightly displaced in d in order to avoid overlapping. In the lower panels, ionic and total abundance profiles for He, O, N, Ne, Ar, and S are shown. The explanation of the symbols used is given in the Legenda at the bottom of the figure. Above the uppermost right box, the limits of the regions into which the slit was divided are indicated by horizontal "errorbars".