The electromagnetic interaction between the spectator system and the charged mesons produced in the course of the high energy heavy ion collision was studied exper- imentally and theoretically in earlier works (1,2). This e ect was found to result in very large distortions of the final state spectra of the produced mesons (3) and to bring new information on the space-time evolution of the non-perturbative meson production pro- cess (4). In this paper a more extended analysis of this e ect will be presented, including a comparative study between charged meson spectra produced in Pb+Pb collisions as well as collisions of Pb ions with smaller nuclei. The experimental results will be compared with Monte Carlo simulations, giving a fair overall understanding of the interplay between the strong and the electromagnetic interaction in the heavy ion collision. A universal be- haviour of charged meson spectra emerges from the above comparative study. This gives a unique chance of using the spectator charge as a tool to study the space-time evolution of the high energy nucleus-nucleus reaction.